JS: Iterator.prototype.map

(new in JS: ECMAScript 2025)

iterator.map(f)

• Apply function f to every yield in Iterator iterator.
• Return a new Generator.

Normally you can use this method on any Iterable, because all standard iterable objects are also Iterator.

• f is given args:
• currentElement
• currentIndex

similar to JS: Array.prototype.map

// define a generator function
function* gf() {
  for (let x of [0, 1, 2, 3, 4]) yield x;
}

// create a generator
const gg = gf();

// use method map
const hh = gg.map((x, i) => [x, i]);

// convert to array
console.log(
  JSON.stringify(Array.from(hh)) === "[[0,0],[1,1],[2,2],[3,3],[4,4]]",
);
// true

// result is both iterable and iterator
console.log(Reflect.has(hh, Symbol.iterator));
console.log(Reflect.has(hh, "next"));