TypeScript allows you to suppress all errors on a line by placing a single-line comment 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.

Bad Practice

// @ts-ignore
const str: 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];
};

Recommended

// @ts-expect-error
const str: string = 1;

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

CIDARLAB / 3DuF

No ignore rules found