JavaScript: Map.prototype.keys
New in JS2015.
mapObj.keys()
- Return a Iterable Object (also is a Iterator) for the keys in the map instance mapObj.
const xx = new Map([[3, "n3"], [4, "n4"], [5, "n5"]]); for (let k of xx.keys()) console.log(k); // 3 // 4 // 5 for (let [k, v] of xx) console.log(k, v); // 3 n3 // 4 n4 // 5 n5
This example shows the result is iterator and iterable:
const xx = new Map([[1, 2], [3, 4]]); console.log(xx.keys); // [Function: keys] // result is a function that returns a iterator object // call it console.log(xx.keys()); // MapIterator { 1, 3 } // result is a iterator object // is also a iterable console.log( Symbol.iterator in (xx.keys()), );