typescript eslint unsafe assignment of an any value

TypeScript ESLint: Unsafe assignment of an any value [Fix]

Last updated: Feb 29, 2024 Reading time · 5 min

# TypeScript ESLint: Unsafe assignment of an any value

The error "@typescript-eslint/no-unsafe-assignment: Unsafe assignment of an any value." occurs when you assign a value with a type of any to a variable or a property.

To solve the error, set the variable to a specific type or disable the ESLint rule.

Here are some examples of when the ESLint error is raised.

All of the assignments above cause the error because the ESLint rule prevents you from assigning a value with an any type to a variable.

The any type effectively turns off type checking and should be used sparingly.

This article addresses 2 similar ESLint errors:

• @typescript-eslint/no-unsafe-assignment: Unsafe assignment of an any value.
• Unexpected any. Specify a different type. eslint@typescript-eslint/no-explicit-any

# Disabling the @typescript-eslint/no-unsafe-assignment ESLint rule

One way to get around the ESLint error is to disable the rule.

For example, the following comment disables the rule for 1 line.

If you need to disable the @typescript-eslint/no-explicit-any rule for a single line, use the following comment.

If you need to disable multiple rules for a line, separate them by a comma.

If you need to disable the rule for the entire file, use the following comment.

If you need to disable the @typescript-eslint/no-explicit-any rule for the entire file, use the following comment instead.

You can disable both rules for the entire file by using the following comment.

If you want to disable the rules globally, add the following 2 rules to your .eslintrc.js file.

If you use a .eslintrc.json file, make sure to double-quote the keys and values.

# Setting the variable or property to unknown instead of any

Alternatively, you can set the variable or property to unknown to resolve the ESLint error.

The unknown type is the type-safe counterpart of any .

When working with the unknown type, we basically tell TypeScript that we're going to get this value, but we don't know its type.

We are going to check with a couple of if statements to track the type down and use it safely.

I have written a detailed guide on how to check the type of a variable in TypeScript .

When using the unknown type, you have to use an if statement as a type guard to check the type of the variable before you are able to use any type-specific methods (e.g. string, array, object, etc).

# The error commonly occurs when parsing a JSON string

The error commonly occurs when parsing a JSON string with the JSON.parse() method.

The result variable stores a value of any type because TypeScript doesn't know the type of the value that is being parsed.

One way to resolve the issue is to use a type predicate .

The value is Employee syntax is called a type predicate.

Our function basically checks if the passed-in value is compatible with an object of type Employee .

Notice that in the if block in which we called the isAnEmployee() function, the parsed variable is typed as Employee and we can access the id and name properties without getting TypeScript or ESLint errors.

I've written a detailed guide on how to check if a value is an object .

# Resolve the issue by typing the variable explicitly

You can also resolve the issue by typing the variable explicitly and removing the any type.

Here is an example of typing an object.

And here is an example of typing an array of objects.

You might have to use a type assertion, e.g. when parsing a JSON string.

In some rare cases, you might have to widen the type to unknown before using a type assertion to set a more specific type.

I've written detailed guides on:

• How to initialize a typed Empty Object in TypeScript
• Declare an Empty Array for a typed Variable in TypeScript
• How to add Elements to an Array in TypeScript
• Check if an Array contains a Value in TypeScript
• Check if a Value is an Array (of type) in TypeScript
• How to declare an Array of Objects in TypeScript
• How to declare a Two-dimensional Array in TypeScript
• Declare Array of Numbers, Strings or Booleans in TypeScript
• Create an Object based on an Interface in TypeScript
• Create a Type from an object's Keys or Values in TypeScript
• ESLint: Expected property shorthand object-shorthand [Fixed]
• 'X' should be listed in the project's dependencies, not devDependencies
• ESLint: Unexpected lexical declaration in case block [Fixed]
• ESLint couldn't find the config 'prettier' to extend from
• Import in body of module reorder to top eslint import/first
• ESLint: A form label must be associated with a control

Borislav Hadzhiev

Web Developer

Copyright © 2024 Borislav Hadzhiev

no-unsafe-argument

Disallow calling a function with a value with type any .

Extending "plugin:@typescript-eslint/ recommended-type-checked " in an ESLint configuration enables this rule.

This rule requires type information to run.

The any type in TypeScript is a dangerous "escape hatch" from the type system. Using any disables many type checking rules and is generally best used only as a last resort or when prototyping code.

Despite your best intentions, the any type can sometimes leak into your codebase. Calling a function with an any typed argument creates a potential safety hole and source of bugs.

This rule disallows calling a function with any in its arguments. That includes spreading arrays or tuples with any typed elements as function arguments.

This rule also compares generic type argument types to ensure you don't pass an unsafe any in a generic position to a receiver that's expecting a specific type. For example, it will error if you pass Set<any> as an argument to a parameter declared as Set<string> .

Try this rule in the playground ↗

• ❌ Incorrect

There are cases where the rule allows passing an argument of any to unknown .

Example of any to unknown assignment that are allowed:

This rule is not configurable.

When Not To Use It ​

If your codebase has many existing any s or areas of unsafe code, it may be difficult to enable this rule. It may be easier to skip the no-unsafe-* rules pending increasing type safety in unsafe areas of your project. You might consider using ESLint disable comments for those specific situations instead of completely disabling this rule.

Related To ​

• no-explicit-any
• no-unsafe-assignment
• no-unsafe-call
• no-unsafe-member-access
• no-unsafe-return

Resources ​

• Rule source
• Test source
• When Not To Use It

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15分調べてもわからないことは、質問しよう！.

TypeScriptは、マイクロソフトによって開発された フリーでオープンソースのプログラミング言語です。 TypeScriptは、JavaScriptの構文の拡張であるので、既存の JavaScriptのコードにわずかな修正を加えれば動作します。

Importした型定義でeslintのUnsafe assignment of an `any` value.が出てしまう

投稿 2021/10/02 07:23

以下のファイルで型定義をして

以下のファイルでimportして使っているのですが、

以下のようなeslintエラーが出てしまいます。

Unsafe assignment of an any value.eslint@typescript-eslint/no-unsafe-assignment

(property) Expense.IFetchedExpense.updated_at: Date

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こちら の条件を満たす必要があります。

export = Expense の記法がよくないです。 以下のように修正すればよいかと。

ただ namespace を export すると利用側は Expense.IFetchedExpense Expense.IExpense のように名前空間から記載する必要があります。 他のインターフェイスと名前が重複しないのであれば、以下のように直接 interface を export するのがよいかと思います。

投稿 2021/10/03 06:51

2021/10/08 01:51

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Bug: object-shorthand loses type parameters when auto-fixing #18429

aldeed commented May 7, 2024

nzakas commented May 8, 2024

• 🎉 1 reaction

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