Typescript: Exploring the Assignability of Numbers, Strings, and More to Null

Why does TypeScript display errors only when assigning a string to a number, but not when assigning null to a number?

export type ArrayWithNumberOrString = Array<number | string>;
export type ArrayWithNumberOrNull = Array<number | null>;


function doSomethingWithNumbersOnly(array: number[]): number[] {
  return array;
};

const numbersAndString: ArrayWithNumberOrString = [1, 2, 3, 'string'];
const numbersAndNull: ArrayWithNumberOrNull = [1, 2, 3, null];

doSomethingWithNumbersOnly(numbersAndString);
doSomethingWithNumbersOnly(numbersAndNull);

Typescript sandbox

Answer №1

Without hesitation, the solution was discovered:

The setting strictNullChecks is not enabled by default in tsconfig.json.

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