Never type

The never type represents values that never occur. It is used to denote functions or expressions that never return or throw an error.

For instance an infinite loop:

const infiniteLoop = (): never => {
    while (true) {
        // do something
    }
};

Throwing an error:

const throwError = (message: string): never => {
    throw new Error(message);
};

The never type is useful in ensuring type safety and catching potential errors in your code. It helps TypeScript analyze and infer more precise types when used in combination with other types and control flow statements, for instance:

type Direction = 'up' | 'down';
const move = (direction: Direction): void => {
    switch (direction) {
        case 'up':
            // move up
            break;
        case 'down':
            // move down
            break;
        default:
            const exhaustiveCheck: never = direction;
            throw new Error(`Unhandled direction: ${exhaustiveCheck}`);
    }
};