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Assignment operators assign values to JavaScript variables.

Shift Assignment Operators

Bitwise assignment operators, logical assignment operators, the = operator.

The Simple Assignment Operator assigns a value to a variable.

Simple Assignment Examples

The += operator.

The Addition Assignment Operator adds a value to a variable.

Addition Assignment Examples

The -= operator.

The Subtraction Assignment Operator subtracts a value from a variable.

Subtraction Assignment Example

The *= operator.

The Multiplication Assignment Operator multiplies a variable.

Multiplication Assignment Example

The **= operator.

The Exponentiation Assignment Operator raises a variable to the power of the operand.

Exponentiation Assignment Example

The /= operator.

The Division Assignment Operator divides a variable.

Division Assignment Example

The %= operator.

The Remainder Assignment Operator assigns a remainder to a variable.

Remainder Assignment Example

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The <<= Operator

The Left Shift Assignment Operator left shifts a variable.

Left Shift Assignment Example

The >>= operator.

The Right Shift Assignment Operator right shifts a variable (signed).

Right Shift Assignment Example

The >>>= operator.

The Unsigned Right Shift Assignment Operator right shifts a variable (unsigned).

Unsigned Right Shift Assignment Example

The &= operator.

The Bitwise AND Assignment Operator does a bitwise AND operation on two operands and assigns the result to the the variable.

Bitwise AND Assignment Example

The |= operator.

The Bitwise OR Assignment Operator does a bitwise OR operation on two operands and assigns the result to the variable.

Bitwise OR Assignment Example

The ^= operator.

The Bitwise XOR Assignment Operator does a bitwise XOR operation on two operands and assigns the result to the variable.

Bitwise XOR Assignment Example

The &&= operator.

The Logical AND assignment operator is used between two values.

If the first value is true, the second value is assigned.

Logical AND Assignment Example

The &&= operator is an ES2020 feature .

The ||= Operator

The Logical OR assignment operator is used between two values.

If the first value is false, the second value is assigned.

Logical OR Assignment Example

The ||= operator is an ES2020 feature .

The ??= Operator

The Nullish coalescing assignment operator is used between two values.

If the first value is undefined or null, the second value is assigned.

Nullish Coalescing Assignment Example

The ??= operator is an ES2020 feature .

Test Yourself With Exercises

Use the correct assignment operator that will result in x being 15 (same as x = x + y ).

Start the Exercise

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• Expressions and operators
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Left-hand-side expressions

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This chapter describes JavaScript's expressions and operators, including assignment, comparison, arithmetic, bitwise, logical, string, ternary and more.

A complete and detailed list of operators and expressions is also available in the reference .

JavaScript has the following types of operators. This section describes the operators and contains information about operator precedence.

• Assignment operators
• Comparison operators
• Arithmetic operators
• Bitwise operators

Logical operators

String operators, conditional (ternary) operator.

• Comma operator

Unary operators

• Relational operator

JavaScript has both binary and unary operators, and one special ternary operator, the conditional operator. A binary operator requires two operands, one before the operator and one after the operator:

For example, 3+4 or x*y .

A unary operator requires a single operand, either before or after the operator:

For example, x++ or ++x .

An assignment operator assigns a value to its left operand based on the value of its right operand. The simple assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x .

There are also compound assignment operators that are shorthand for the operations listed in the following table:

Destructuring

For more complex assignments, the destructuring assignment syntax is a JavaScript expression that makes it possible to extract data from arrays or objects using a syntax that mirrors the construction of array and object literals.

A comparison operator compares its operands and returns a logical value based on whether the comparison is true. The operands can be numerical, string, logical, or object values. Strings are compared based on standard lexicographical ordering, using Unicode values. In most cases, if the two operands are not of the same type, JavaScript attempts to convert them to an appropriate type for the comparison. This behavior generally results in comparing the operands numerically. The sole exceptions to type conversion within comparisons involve the === and !== operators, which perform strict equality and inequality comparisons. These operators do not attempt to convert the operands to compatible types before checking equality. The following table describes the comparison operators in terms of this sample code:

Note:  ( => ) is not an operator, but the notation for Arrow functions .

An arithmetic operator takes numerical values (either literals or variables) as their operands and returns a single numerical value. The standard arithmetic operators are addition ( + ), subtraction ( - ), multiplication ( * ), and division ( / ). These operators work as they do in most other programming languages when used with floating point numbers (in particular, note that division by zero produces Infinity ). For example:

In addition to the standard arithmetic operations (+, -, * /), JavaScript provides the arithmetic operators listed in the following table:

A bitwise operator treats their operands as a set of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values.

The following table summarizes JavaScript's bitwise operators.

Bitwise logical operators

Conceptually, the bitwise logical operators work as follows:

• The operands are converted to thirty-two-bit integers and expressed by a series of bits (zeros and ones). Numbers with more than 32 bits get their most significant bits discarded. For example, the following integer with more than 32 bits will be converted to a 32 bit integer: Before: 11100110111110100000000000000110000000000001 After: 10100000000000000110000000000001
• Each bit in the first operand is paired with the corresponding bit in the second operand: first bit to first bit, second bit to second bit, and so on.
• The operator is applied to each pair of bits, and the result is constructed bitwise.

For example, the binary representation of nine is 1001, and the binary representation of fifteen is 1111. So, when the bitwise operators are applied to these values, the results are as follows:

Note that all 32 bits are inverted using the Bitwise NOT operator, and that values with the most significant (left-most) bit set to 1 represent negative numbers (two's-complement representation).

Bitwise shift operators

The bitwise shift operators take two operands: the first is a quantity to be shifted, and the second specifies the number of bit positions by which the first operand is to be shifted. The direction of the shift operation is controlled by the operator used.

Shift operators convert their operands to thirty-two-bit integers and return a result of the same type as the left operand.

The shift operators are listed in the following table.

Logical operators are typically used with Boolean (logical) values; when they are, they return a Boolean value. However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value. The logical operators are described in the following table.

Examples of expressions that can be converted to false are those that evaluate to null, 0, NaN, the empty string (""), or undefined.

The following code shows examples of the && (logical AND) operator.

The following code shows examples of the || (logical OR) operator.

The following code shows examples of the ! (logical NOT) operator.

Short-circuit evaluation

As logical expressions are evaluated left to right, they are tested for possible "short-circuit" evaluation using the following rules:

• false && anything is short-circuit evaluated to false.
• true || anything is short-circuit evaluated to true.

The rules of logic guarantee that these evaluations are always correct. Note that the anything part of the above expressions is not evaluated, so any side effects of doing so do not take effect.

In addition to the comparison operators, which can be used on string values, the concatenation operator (+) concatenates two string values together, returning another string that is the union of the two operand strings.

For example,

The shorthand assignment operator += can also be used to concatenate strings.

The conditional operator is the only JavaScript operator that takes three operands. The operator can have one of two values based on a condition. The syntax is:

If condition is true, the operator has the value of val1 . Otherwise it has the value of val2 . You can use the conditional operator anywhere you would use a standard operator.

This statement assigns the value "adult" to the variable status if age is eighteen or more. Otherwise, it assigns the value "minor" to status .

The comma operator ( , ) simply evaluates both of its operands and returns the value of the last operand. This operator is primarily used inside a for loop, to allow multiple variables to be updated each time through the loop.

For example, if a is a 2-dimensional array with 10 elements on a side, the following code uses the comma operator to update two variables at once. The code prints the values of the diagonal elements in the array:

A unary operation is an operation with only one operand.

The delete operator deletes an object, an object's property, or an element at a specified index in an array. The syntax is:

where objectName is the name of an object, property is an existing property, and index is an integer representing the location of an element in an array.

The fourth form is legal only within a with statement, to delete a property from an object.

You can use the delete operator to delete variables declared implicitly but not those declared with the var statement.

If the delete operator succeeds, it sets the property or element to undefined . The delete operator returns true if the operation is possible; it returns false if the operation is not possible.

Deleting array elements

When you delete an array element, the array length is not affected. For example, if you delete a[3] , a[4] is still a[4] and a[3] is undefined.

When the delete operator removes an array element, that element is no longer in the array. In the following example, trees[3] is removed with delete . However, trees[3] is still addressable and returns undefined .

If you want an array element to exist but have an undefined value, use the undefined keyword instead of the delete operator. In the following example, trees[3] is assigned the value undefined , but the array element still exists:

The typeof operator is used in either of the following ways:

The typeof operator returns a string indicating the type of the unevaluated operand. operand is the string, variable, keyword, or object for which the type is to be returned. The parentheses are optional.

Suppose you define the following variables:

The typeof operator returns the following results for these variables:

For the keywords true and null , the typeof operator returns the following results:

For a number or string, the typeof operator returns the following results:

For property values, the typeof operator returns the type of value the property contains:

For methods and functions, the typeof operator returns results as follows:

For predefined objects, the typeof operator returns results as follows:

The void operator is used in either of the following ways:

The void operator specifies an expression to be evaluated without returning a value. expression is a JavaScript expression to evaluate. The parentheses surrounding the expression are optional, but it is good style to use them.

You can use the void operator to specify an expression as a hypertext link. The expression is evaluated but is not loaded in place of the current document.

The following code creates a hypertext link that does nothing when the user clicks it. When the user clicks the link, void(0) evaluates to undefined , which has no effect in JavaScript.

The following code creates a hypertext link that submits a form when the user clicks it.

Relational operators

A relational operator compares its operands and returns a Boolean value based on whether the comparison is true.

The in operator returns true if the specified property is in the specified object. The syntax is:

where propNameOrNumber is a string or numeric expression representing a property name or array index, and objectName is the name of an object.

The following examples show some uses of the in operator.

The instanceof operator returns true if the specified object is of the specified object type. The syntax is:

where objectName is the name of the object to compare to objectType , and objectType is an object type, such as Date or Array .

Use instanceof when you need to confirm the type of an object at runtime. For example, when catching exceptions, you can branch to different exception-handling code depending on the type of exception thrown.

For example, the following code uses instanceof to determine whether theDay is a Date object. Because theDay is a Date object, the statements in the if statement execute.

The precedence of operators determines the order they are applied when evaluating an expression. You can override operator precedence by using parentheses.

The following table describes the precedence of operators, from highest to lowest.

A more detailed version of this table, complete with links to additional details about each operator, may be found in JavaScript Reference .

• Expressions

An expression is any valid unit of code that resolves to a value.

Every syntactically valid expression resolves to some value but conceptually, there are two types of expressions: with side effects (for example: those that assign value to a variable) and those that in some sense evaluates and therefore resolves to value.

The expression x = 7 is an example of the first type. This expression uses the = operator to assign the value seven to the variable x . The expression itself evaluates to seven.

The code 3 + 4 is an example of the second expression type. This expression uses the + operator to add three and four together without assigning the result, seven, to a variable. JavaScript has the following expression categories:

• Arithmetic: evaluates to a number, for example 3.14159. (Generally uses arithmetic operators .)
• String: evaluates to a character string, for example, "Fred" or "234". (Generally uses string operators .)
• Logical: evaluates to true or false. (Often involves logical operators .)
• Primary expressions: Basic keywords and general expressions in JavaScript.
• Left-hand-side expressions: Left values are the destination of an assignment.

Primary expressions

Basic keywords and general expressions in JavaScript.

Use the this keyword to refer to the current object. In general, this refers to the calling object in a method. Use this either with the dot or the bracket notation:

Suppose a function called validate validates an object's value property, given the object and the high and low values:

You could call validate in each form element's onChange event handler, using this to pass it the form element, as in the following example:

• Grouping operator

The grouping operator ( ) controls the precedence of evaluation in expressions. For example, you can override multiplication and division first, then addition and subtraction to evaluate addition first.

Comprehensions

Comprehensions are an experimental JavaScript feature, targeted to be included in a future ECMAScript version. There are two versions of comprehensions:

Comprehensions exist in many programming languages and allow you to quickly assemble a new array based on an existing one, for example.

Left values are the destination of an assignment.

You can use the new operator to create an instance of a user-defined object type or of one of the built-in object types. Use new as follows:

The super keyword is used to call functions on an object's parent. It is useful with classes to call the parent constructor, for example.

Spread operator

The spread operator allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.

Example: Today if you have an array and want to create a new array with the existing one being part of it, the array literal syntax is no longer sufficient and you have to fall back to imperative code, using a combination of push , splice , concat , etc. With spread syntax this becomes much more succinct:

Similarly, the spread operator works with function calls:

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• Assignment operators

An assignment operator assigns a value to its left operand based on the value of its right operand.

The basic assignment operator is equal ( = ), which assigns the value of its right operand to its left operand. That is, x = y assigns the value of y to x . The other assignment operators are usually shorthand for standard operations, as shown in the following definitions and examples.

Simple assignment operator which assigns a value to a variable. Chaining the assignment operator is possible in order to assign a single value to multiple variables. See the example.

Addition assignment

The addition assignment operator adds the value of the right operand to a variable and assigns the result to the variable. The types of the two operands determine the behavior of the addition assignment operator. Addition or concatenation is possible. See the addition operator for more details.

Subtraction assignment

The subtraction assignment operator subtracts the value of the right operand from a variable and assigns the result to the variable. See the subtraction operator for more details.

Multiplication assignment

The multiplication assignment operator multiplies a variable by the value of the right operand and assigns the result to the variable. See the multiplication operator for more details.

Division assignment

The division assignment operator divides a variable by the value of the right operand and assigns the result to the variable. See the division operator for more details.

Remainder assignment

The remainder assignment operator divides a variable by the value of the right operand and assigns the remainder to the variable. See the remainder operator for more details.

Left shift assignment

The left shift assignment operator moves the specified amount of bits to the left and assigns the result to the variable. See the left shift operator for more details.

Right shift assignment

The right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the right shift operator for more details.

Unsigned right shift assignment

The unsigned right shift assignment operator moves the specified amount of bits to the right and assigns the result to the variable. See the unsigned right shift operator for more details.

Bitwise AND assignment

The bitwise AND assignment operator uses the binary representation of both operands, does a bitwise AND operation on them and assigns the result to the variable. See the bitwise AND operator for more details.

Bitwise XOR assignment

The bitwise XOR assignment operator uses the binary representation of both operands, does a bitwise XOR operation on them and assigns the result to the variable. See the bitwise XOR operator for more details.

Bitwise OR assignment

The bitwise OR assignment operator uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable. See the bitwise OR operator for more details.

Left operand with another assignment operator

In unusual situations, the assignment operator (e.g. x += y ) is not identical to the meaning expression (here x = x + y ). When the left operand of an assignment operator itself contains an assignment operator, the left operand is evaluated only once. For example:

Specifications

Browser compatibility.

• Arithmetic operators

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What is Multiplication Assignment Operator (*=) in JavaScript?

In this article, we will learn about the Multiplication assignment operator (*=) in JavaScript. In general, we use a = a * b this expression to update the value of a variable with the value returned after multiplying its original value with some other value, which is easy to understand, but it time taking to write again and again if we are using updating values of more variables like this. So, to overcome this problem, JavaScript introduces us to the multiplication assignment operator (*=) as it is the short form for using the above expression.

The multiplication Assignment operator (*=)

The multiplication assignment operator is a binary assignment operator which means it requires at least one pair of operands to perform the task or to assign the value to the operand. The multiplication assignment operator will multiply the value of the left operand with the value of the right operand and assigns it to the left operand to update its value.

The following syntax will show you how you can use the multiplication assignment (*=) operator to update the value of the left operand −

Let us understand the use or the implementation of the Multiplication Assignment operator (*=) in detail with help of code examples.

Step 1 − In the first step, we will add two input elements with number type in the HTML documents to get numbers input from the user.

Step 2 − In this step, we will add a button with the onclick event which will later call a function when the event is triggered.

Step 3 − In the next step, we will define a JavaScript function and assign it to the onclick event of the button to call it later and display the results to the user.

The below example will explain the use of the multiplication assignment operator (*=) to update the value of the left operand −

In the above example, First, we grabbed both the input elements using their ids and then get their values using the value property and convert them to the number type using the Number() method after performing all these tasks we used the multiplication assignment operator on the val1 variable to update its value with the multiplication result of the two input values as val1 * val2 , then display the result to the user.

Let us see one more example, where one input is of type number while another is of type string.

The algorithm of this example and the above example is the same, you just need to make some changes. You have to replace the input type of one of the input elements to the text, and the rest of the code will remain the same, as done in the below example.

The example below will illustrate the behavior of the multiplication assignment operator when both the operands are of different data types −

In this example, we have used the multiplication assignment operator (*=) with the variables of different data types. In this case, if the value of the string variable is numerical, then the multiplication assignment operator will work similarly as it works in cases when both the variables are of type number. But if the value of the string variable is a word or any string, then it will return NaN as the multiplication result of a number and a string is NaN.

In this tutorial, we have seen what is the multiplication assignment operator in JavaScript and the working of this with help of two different code examples to understand the behavior of the multiplication assignment operator in different conditions. The first example we have taken is showing the behavior of the operator in the case of the number type variables while in the later one we used the multiplication assignment operator with different variables of different data types, where we come to know, that the multiplication assignment operator will not work as expected when a word is multiplied with a number.

Related Articles

• What is Addition Assignment Operator (+=) in JavaScript?
• What is Multiplication Operator (*) in JavaScript?
• What is Bitwise OR Assignment Operator (|=) in JavaScript?
• What is Bitwise XOR Assignment Operator (^=) in JavaScript?
• What is an assignment operator in C#?
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JAVASCRIPT ASSIGNMENT OPERATORS

In this tutorial, you will learn about all the different assignment operators in javascript and how to use them in javascript.

Assignment Operators

In javascript, there are 16 different assignment operators that are used to assign value to the variable. It is shorthand of other operators which is recommended to use.

The assignment operators are used to assign value based on the right operand to its left operand.

The left operand must be a variable while the right operand may be a variable, number, boolean, string, expression, object, or combination of any other.

One of the most basic assignment operators is equal = , which is used to directly assign a value.

Assignment Operators List

Here is the list of all assignment operators in JavaScript:

In the following table if variable a is not defined then assume it to be 10.

Assignment operator

The assignment operator = is the simplest value assigning operator which assigns a given value to a variable.

The assignment operators support chaining, which means you can assign a single value in multiple variables in a single line.

Addition assignment operator

The addition assignment operator += is used to add the value of the right operand to the value of the left operand and assigns the result to the left operand.

On the basis of the data type of variable, the addition assignment operator may add or concatenate the variables.

Subtraction assignment operator

The subtraction assignment operator -= subtracts the value of the right operand from the value of the left operand and assigns the result to the left operand.

If the value can not be subtracted then it results in a NaN .

Multiplication assignment operator

The multiplication assignment operator *= assigns the result to the left operand after multiplying values of the left and right operand.

Division assignment operator

The division assignment operator /= divides the value of the left operand by the value of the right operand and assigns the result to the left operand.

Remainder assignment operator

The remainder assignment operator %= assigns the remainder to the left operand after dividing the value of the left operand by the value of the right operand.

Exponentiation assignment operator

The exponential assignment operator **= assigns the result of exponentiation to the left operand after exponentiating the value of the left operand by the value of the right operand.

Left shift assignment

The left shift assignment operator <<= assigns the result of the left shift to the left operand after shifting the value of the left operand by the value of the right operand.

Right shift assignment

The right shift assignment operator >>= assigns the result of the right shift to the left operand after shifting the value of the left operand by the value of the right operand.

Unsigned right shift assignment

The unsigned right shift assignment operator >>>= assigns the result of the unsigned right shift to the left operand after shifting the value of the left operand by the value of the right operand.

Bitwise AND assignment

The bitwise AND assignment operator &= assigns the result of bitwise AND to the left operand after ANDing the value of the left operand by the value of the right operand.

Bitwise OR assignment

The bitwise OR assignment operator |= assigns the result of bitwise OR to the left operand after ORing the value of left operand by the value of the right operand.

Bitwise XOR assignment

The bitwise XOR assignment operator ^= assigns the result of bitwise XOR to the left operand after XORing the value of the left operand by the value of the right operand.

Logical AND assignment

The logical AND assignment operator &&= assigns value to left operand only when it is truthy .

Note : A truthy value is a value that is considered true when encountered in a boolean context.

Logical OR assignment

The logical OR assignment operator ||= assigns value to left operand only when it is falsy .

Note : A falsy value is a value that is considered false when encountered in a boolean context.

Logical nullish assignment

The logical nullish assignment operator ??= assigns value to left operand only when it is nullish ( null or undefined ).

• Skip to main content

• Multiplication assignment (*=)

The multiplication assignment operator ( *= ) multiplies a variable by the value of the right operand and assigns the result to the variable.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Basic operators, maths

We know many operators from school. They are things like addition + , multiplication * , subtraction - , and so on.

In this chapter, we’ll start with simple operators, then concentrate on JavaScript-specific aspects, not covered by school arithmetic.

Terms: “unary”, “binary”, “operand”

Before we move on, let’s grasp some common terminology.

An operand – is what operators are applied to. For instance, in the multiplication of 5 * 2 there are two operands: the left operand is 5 and the right operand is 2 . Sometimes, people call these “arguments” instead of “operands”.

An operator is unary if it has a single operand. For example, the unary negation - reverses the sign of a number:

An operator is binary if it has two operands. The same minus exists in binary form as well:

Formally, in the examples above we have two different operators that share the same symbol: the negation operator, a unary operator that reverses the sign, and the subtraction operator, a binary operator that subtracts one number from another.

The following math operations are supported:

• Addition + ,
• Subtraction - ,
• Multiplication * ,
• Division / ,
• Remainder % ,
• Exponentiation ** .

The first four are straightforward, while % and ** need a few words about them.

Remainder %

The remainder operator % , despite its appearance, is not related to percents.

The result of a % b is the remainder of the integer division of a by b .

For instance:

Exponentiation **

The exponentiation operator a ** b raises a to the power of b .

In school maths, we write that as a b .

Just like in maths, the exponentiation operator is defined for non-integer numbers as well.

For example, a square root is an exponentiation by ½:

String concatenation with binary +

Let’s meet the features of JavaScript operators that are beyond school arithmetics.

Usually, the plus operator + sums numbers.

But, if the binary + is applied to strings, it merges (concatenates) them:

Note that if any of the operands is a string, then the other one is converted to a string too.

For example:

See, it doesn’t matter whether the first operand is a string or the second one.

Here’s a more complex example:

Here, operators work one after another. The first + sums two numbers, so it returns 4 , then the next + adds the string 1 to it, so it’s like 4 + '1' = '41' .

Here, the first operand is a string, the compiler treats the other two operands as strings too. The 2 gets concatenated to '1' , so it’s like '1' + 2 = "12" and "12" + 2 = "122" .

The binary + is the only operator that supports strings in such a way. Other arithmetic operators work only with numbers and always convert their operands to numbers.

Here’s the demo for subtraction and division:

Numeric conversion, unary +

The plus + exists in two forms: the binary form that we used above and the unary form.

The unary plus or, in other words, the plus operator + applied to a single value, doesn’t do anything to numbers. But if the operand is not a number, the unary plus converts it into a number.

It actually does the same thing as Number(...) , but is shorter.

The need to convert strings to numbers arises very often. For example, if we are getting values from HTML form fields, they are usually strings. What if we want to sum them?

The binary plus would add them as strings:

If we want to treat them as numbers, we need to convert and then sum them:

From a mathematician’s standpoint, the abundance of pluses may seem strange. But from a programmer’s standpoint, there’s nothing special: unary pluses are applied first, they convert strings to numbers, and then the binary plus sums them up.

Why are unary pluses applied to values before the binary ones? As we’re going to see, that’s because of their higher precedence .

Operator precedence

If an expression has more than one operator, the execution order is defined by their precedence , or, in other words, the default priority order of operators.

From school, we all know that the multiplication in the expression 1 + 2 * 2 should be calculated before the addition. That’s exactly the precedence thing. The multiplication is said to have a higher precedence than the addition.

Parentheses override any precedence, so if we’re not satisfied with the default order, we can use them to change it. For example, write (1 + 2) * 2 .

There are many operators in JavaScript. Every operator has a corresponding precedence number. The one with the larger number executes first. If the precedence is the same, the execution order is from left to right.

Here’s an extract from the precedence table (you don’t need to remember this, but note that unary operators are higher than corresponding binary ones):

As we can see, the “unary plus” has a priority of 14 which is higher than the 11 of “addition” (binary plus). That’s why, in the expression "+apples + +oranges" , unary pluses work before the addition.

Let’s note that an assignment = is also an operator. It is listed in the precedence table with the very low priority of 2 .

That’s why, when we assign a variable, like x = 2 * 2 + 1 , the calculations are done first and then the = is evaluated, storing the result in x .

Assignment = returns a value

The fact of = being an operator, not a “magical” language construct has an interesting implication.

All operators in JavaScript return a value. That’s obvious for + and - , but also true for = .

The call x = value writes the value into x and then returns it .

Here’s a demo that uses an assignment as part of a more complex expression:

In the example above, the result of expression (a = b + 1) is the value which was assigned to a (that is 3 ). It is then used for further evaluations.

Funny code, isn’t it? We should understand how it works, because sometimes we see it in JavaScript libraries.

Although, please don’t write the code like that. Such tricks definitely don’t make code clearer or readable.

Chaining assignments

Another interesting feature is the ability to chain assignments:

Chained assignments evaluate from right to left. First, the rightmost expression 2 + 2 is evaluated and then assigned to the variables on the left: c , b and a . At the end, all the variables share a single value.

Once again, for the purposes of readability it’s better to split such code into few lines:

That’s easier to read, especially when eye-scanning the code fast.

Modify-in-place

We often need to apply an operator to a variable and store the new result in that same variable.

This notation can be shortened using the operators += and *= :

Short “modify-and-assign” operators exist for all arithmetical and bitwise operators: /= , -= , etc.

Such operators have the same precedence as a normal assignment, so they run after most other calculations:

Increment/decrement

Increasing or decreasing a number by one is among the most common numerical operations.

So, there are special operators for it:

Increment ++ increases a variable by 1:

Decrement -- decreases a variable by 1:

Increment/decrement can only be applied to variables. Trying to use it on a value like 5++ will give an error.

The operators ++ and -- can be placed either before or after a variable.

• When the operator goes after the variable, it is in “postfix form”: counter++ .
• The “prefix form” is when the operator goes before the variable: ++counter .

Both of these statements do the same thing: increase counter by 1 .

Is there any difference? Yes, but we can only see it if we use the returned value of ++/-- .

Let’s clarify. As we know, all operators return a value. Increment/decrement is no exception. The prefix form returns the new value while the postfix form returns the old value (prior to increment/decrement).

To see the difference, here’s an example:

In the line (*) , the prefix form ++counter increments counter and returns the new value, 2 . So, the alert shows 2 .

Now, let’s use the postfix form:

In the line (*) , the postfix form counter++ also increments counter but returns the old value (prior to increment). So, the alert shows 1 .

To summarize:

If the result of increment/decrement is not used, there is no difference in which form to use:

If we’d like to increase a value and immediately use the result of the operator, we need the prefix form:

If we’d like to increment a value but use its previous value, we need the postfix form:

The operators ++/-- can be used inside expressions as well. Their precedence is higher than most other arithmetical operations.

Compare with:

Though technically okay, such notation usually makes code less readable. One line does multiple things – not good.

While reading code, a fast “vertical” eye-scan can easily miss something like counter++ and it won’t be obvious that the variable increased.

We advise a style of “one line – one action”:

Bitwise operators

Bitwise operators treat arguments as 32-bit integer numbers and work on the level of their binary representation.

These operators are not JavaScript-specific. They are supported in most programming languages.

The list of operators:

• AND ( & )
• LEFT SHIFT ( << )
• RIGHT SHIFT ( >> )
• ZERO-FILL RIGHT SHIFT ( >>> )

These operators are used very rarely, when we need to fiddle with numbers on the very lowest (bitwise) level. We won’t need these operators any time soon, as web development has little use of them, but in some special areas, such as cryptography, they are useful. You can read the Bitwise Operators chapter on MDN when a need arises.

The comma operator , is one of the rarest and most unusual operators. Sometimes, it’s used to write shorter code, so we need to know it in order to understand what’s going on.

The comma operator allows us to evaluate several expressions, dividing them with a comma , . Each of them is evaluated but only the result of the last one is returned.

Here, the first expression 1 + 2 is evaluated and its result is thrown away. Then, 3 + 4 is evaluated and returned as the result.

Please note that the comma operator has very low precedence, lower than = , so parentheses are important in the example above.

Without them: a = 1 + 2, 3 + 4 evaluates + first, summing the numbers into a = 3, 7 , then the assignment operator = assigns a = 3 , and the rest is ignored. It’s like (a = 1 + 2), 3 + 4 .

Why do we need an operator that throws away everything except the last expression?

Sometimes, people use it in more complex constructs to put several actions in one line.

Such tricks are used in many JavaScript frameworks. That’s why we’re mentioning them. But usually they don’t improve code readability so we should think well before using them.

The postfix and prefix forms

What are the final values of all variables a , b , c and d after the code below?

The answer is:

Assignment result

What are the values of a and x after the code below?

• a = 4 (multiplied by 2)
• x = 5 (calculated as 1 + 4)

Type conversions

What are results of these expressions?

Think well, write down and then compare with the answer.

• The addition with a string "" + 1 converts 1 to a string: "" + 1 = "1" , and then we have "1" + 0 , the same rule is applied.
• The subtraction - (like most math operations) only works with numbers, it converts an empty string "" to 0 .
• The addition with a string appends the number 5 to the string.
• The subtraction always converts to numbers, so it makes " -9 " a number -9 (ignoring spaces around it).
• null becomes 0 after the numeric conversion.
• undefined becomes NaN after the numeric conversion.
• Space characters are trimmed off string start and end when a string is converted to a number. Here the whole string consists of space characters, such as \t , \n and a “regular” space between them. So, similarly to an empty string, it becomes 0 .

Fix the addition

Here’s a code that asks the user for two numbers and shows their sum.

It works incorrectly. The output in the example below is 12 (for default prompt values).

Why? Fix it. The result should be 3 .

The reason is that prompt returns user input as a string.

So variables have values "1" and "2" respectively.

What we should do is to convert strings to numbers before + . For example, using Number() or prepending them with + .

For example, right before prompt :

Or in the alert :

Using both unary and binary + in the latest code. Looks funny, doesn’t it?

• If you have suggestions what to improve - please submit a GitHub issue or a pull request instead of commenting.
• If you can't understand something in the article – please elaborate.
• To insert few words of code, use the <code> tag, for several lines – wrap them in <pre> tag, for more than 10 lines – use a sandbox ( plnkr , jsbin , codepen …)

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JavaScript Program for Multiplication of Two Numbers

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In this article, we are going to learn how we can multiply two numbers using JavaScript. Multiplying the two numbers in JavaScript involves performing arithmetic addition on numeric values, resulting in their sum.

JavaScript supports numeric data types. In JavaScript, both floating-point and integer numbers fall under the same “Number” type. Because JavaScript takes care of it for you, you don’t need to explicitly declare whether a number is an integer or a floating-point number. In order to avoid having to declare them separately, we can use a variable and assign it to any value.

These are the following ways by which we can multiply two numbers:

Table of Content

Using “*” operator, using functions, using arrow function.

• Using Multiplication assignment operator
• Using for loop

In this approach we multiply two numbers in JavaScript involves using the * operator to perform arithmetic multiplication on numeric variables, resulting in their result.

Functions are the building blocks of some specific code that carry out specific tasks. Using the function, we can multiply two numbers by passing parameters, and the function will then return the result of the multiplication.

Example: This example describes the multiplication of 2 numbers using Function.

In order to multiply two numbers, we create an arrow function , passing the values of the two numbers as parameters and returning the result of multiplication. We obtain the multiplied value by calling the arrow function and providing values for the parameter.

Example: This example describes the multiplication of 2 numbers using Arrow function.

Using Multiplication Assignment Operator

When multiplying a variable by a specific amount and returning the result to the variable, the multiplication assignment operator *= is a useful shorthand. In JavaScript, it is a compound assignment operator.

Example: This example is describing how we can multiply two number using multiplication assignment operator.

Using for Loop

We can multiply two numbers by using for loop . A function must first be initialized before multiplication calculations can be made using a for loop.

Example: This examples describes how we can multiply two numbers using for loop

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