E0240: '!' is not allowed on methods

In TypeScript, ! after a field name indicates a definite assignment assertion. Because ! only applies to fields, is a syntax error to write ! after a method name:

class Banana {
  skin!: BananaSkin | undefined;

  peel!() {
    this.skin = undefined;
  }
}

To fix this error, remove the !:

class Banana {
  skin!: BananaSkin | undefined;

  peel() {
    this.skin = undefined;
  }
}

Introduced in quick-lint-js version 2.6.0.

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