Disable type checking for a File or a Line in TypeScript

# Table of Contents

1. Disable type checking for an entire File in TypeScript
2. Disable type checking for a Line in TypeScript
3. Disable type checking for JavaScript files in TypeScript
4. Disable type checking for node_modules in TypeScript

# Disable type checking for an entire File in TypeScript

Use the // @ts-nocheck comment to disable type checking for an entire file in TypeScript.

The // @ts-nocheck comment instructs TypeScript to skip the file when type checking.

If you use a linter, you might need to disable it on the line of the comment.

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// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-nocheck

console.log('no errors' / 0);
console.log('no errors' / 0);

If you need to disable type checking for JavaScript files in TypeScript, scroll down to the next subheading.

The @ts-nocheck comment disables type checking for the entire file.

The // @ts-nocheck comment has to be placed at the top of your file.

# Disable type checking for a Line in TypeScript

Use the // @ts-ignore comment to disable type checking for a line in TypeScript.

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// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-ignore
console.log('no error' / 0);

The // @ts-ignore comment disables all type checking for the next line.

You might also see the @ts-expect-error comment used to disable type checking for the next line.

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// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-expect-error
console.log('hello world' / 0);

The // @ts-expect-error will suppress any type errors on the next line, but if there aren't any errors, TypeScript will inform us that using @ts-expect-error was unnecessary.

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// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-expect-error
console.log('hello world' / 0);

// ⛔️ Error: Unused '@ts-expect-error' directive.ts(2578)
// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-expect-error
console.log(100 * 100);

That's the main difference between ts-ignore and ts-expect-error - // @ts-ignore doesn't alert us if the next line has no errors.

An example of when you would use the // @ts-expect-error comment is when you have a function that takes a parameter of a specific type but you want to test that it works as expected when passing a parameter of a different type.

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function sum(a: number, b: number) {
  if (typeof a !== 'number' || typeof b !== 'number') {
    return 0;
  }

  return a + b;
}

// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-expect-error
const result = sum('hello', 'world');

if (result === 0) {
  console.log('✅ Test passes');
}

The sum function in the example takes 2 numbers as parameters, but we want to test if it works as expected when passed parameters of a different type.

Using this approach, we can test our function and would get a TypeScript error if the // @ts-expect-error comment was unnecessary.

# Disable type checking for JavaScript files in TypeScript

Use the // @ts-nocheck comment to disable all type checking in a TypeScript file.

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// 👇️ ts-nocheck disables type checking for the entire file
// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-nocheck

// 👇️ ts-ignore ignores any ts errors on the next line
// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-ignore
function multiply(a, b) {
  return a * b;
}

The @ts-nocheck comment disables type checking for an entire file.

If you need to disable all type checking for JavaScript files, you have to set the checkJs option to false in your tsconfig.json file.

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{
  "compilerOptions": {
    "allowJs": true,
    "checkJs": false,
    // ... your other options
  }
}

The allowJs option allows you to import JavaScript files in your TypeScript project.

When the checkJs option is enabled, errors are reported in all JavaScript files in your project.

If you only want to disable type checking for a single line, you can use the // @ts-ignore comment.

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// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-ignore
function multiply(a, b) {
  return a * b;
}

The // @ts-ignore comment disables all type checking errors on the next line.

If you use a linter, chances are you have to disable it for the line on which you use @ts-ignore because most linters have rules against using ts comments.

# Disable type checking for node_modules in TypeScript

To disable type checking for node_modules in TypeScript, set the skipLibCheck property to true in your tsconfig.json file.

Open your tsconfig.json file and set the skipLibCheck property to true.

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{
  "compilerOptions": {
    "skipLibCheck": true,
    // ... other settings
  }
}

The skipLibCheck option instructs the TypeScript compiler to skip type checking for declaration (.d.ts) files.

You can achieve the same result by passing the --skipLibCheck flag when using the command line.

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tsc --skipLibCheck

# Make sure node-modules is in your exclude array

If the errors are not resolved, make sure that the exclude array in your tsconfig.json file contains the path to your node_modules directory.

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{
  "compilerOptions": {
    "skipLibCheck": true,
    // ... other settings
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

Make sure that you're using a recent version of TypeScript as the skipLibCheck option doesn't work in some older versions.

When the skipLibCheck option is set to false, you often encounter issues when there are multiple copies of a library's types in your node_modules directory.

It also might be that two libraries define copies of the same type in an inconsistent way.

When skipLibCheck is set to true, you often end up saving time during compilation.

Even though the setting disables type checking for d.ts files, TypeScript still type checks the code you specifically refer to in your application's source code.