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prefer-ts-expect-error

Recommends using @ts-expect-error over @ts-ignore.

TypeScript allows you to suppress all errors on a line by placing a single-line comment or a comment block line starting with @ts-ignore immediately before the erroring line. While powerful, there is no way to know if a @ts-ignore is actually suppressing an error without manually investigating what happens when the @ts-ignore is removed.

This means its easy for @ts-ignores to be forgotten about, and remain in code even after the error they were suppressing is fixed. This is dangerous, as if a new error arises on that line it'll be suppressed by the forgotten about @ts-ignore, and so be missed.

To address this, TS3.9 ships with a new single-line comment directive: // @ts-expect-error.

This directive operates in the same manner as @ts-ignore, but will error if the line it's meant to be suppressing doesn't actually contain an error, making it a lot safer.

Rule Details​

This rule looks for usages of @ts-ignore, and flags them to be replaced with @ts-expect-error.

Examples of code for this rule:

// @ts-ignore
const str: string = 1;

/**
 * Explaining comment
 *
 * @ts-ignore */
const multiLine: number = 'value';

/** @ts-ignore */
const block: string = 1;

const isOptionEnabled = (key: string): boolean => {
  // @ts-ignore: if key isn't in globalOptions it'll be undefined which is false
  return !!globalOptions[key];
};

Options​

// .eslintrc.json
{
  "rules": {
    "@typescript-eslint/prefer-ts-expect-error": "warn"
  }
}

This rule is not configurable.

When Not To Use It​

If you are NOT using TypeScript 3.9 (or greater), then you will not be able to use this rule, as the directive is not supported

Further Reading​

Attributes​

  • Configs:
    • ✅ Recommended
    • 🔒 Strict
  • 🔧 Fixable
  • 💭 Requires type information