What is the the ??= operator in typescript called?

The range function in the Lit Element repository uses this operator ??= … Which looks like the nullish coalescing operator with an equal sign … what is it called?

Here is the entire code snippet for reference.

/**
 * Returns an iterable of integers from `start` to `end` (exclusive)
 * incrementing by `step`.
 *
 * If `start` is omitted, the range starts at `0`. `step` defaults to `1`.
 *
 * @example
 *
 * ```ts
 * render() {
 *   return html`
 *     ${map(range(8), () => html`<div class="cell"></div>`)}
 *   `;
 * }
 * ```
 */
export function range(end: number): Iterable<number>;
export function range(
  start: number,
  end: number,
  step?: number,
): Iterable<number>;
export function* range(startOrEnd: number, end?: number, step = 1) {
  const start = end === undefined ? 0 : startOrEnd;
  end ??= startOrEnd;
  for (let i = start; step > 0 ? i < end : end < i; i += step) {
    yield i;
  }
}

>Solution :

The ??= operator in JavaScript is called the nullish coalescing assignment operator.
It is a shorthand operator in JavaScript that assigns a value to a variable if the variable is null or undefined. This operator is useful for concisely providing default values.

let x;
 x ??= "default";