JavaScript Map keys()
Example
// Create a Map
const fruits = new Map([
["apples", 500],
["bananas", 300],
["oranges", 200]
]);
// List all Keys
let text = "";
for (const x of fruits.keys()) {
text += x;
}
Try it Yourself »
const fruits = new Map([
["apples", 500],
["bananas", 300],
["oranges", 200]
]);
// List all Keys
let text = "";
for (const x of fruits.keys()) {
text += x;
}
More Examples Below !
Description
The keys() method returns an iterator object with the keys in a map:
The keys() method does not change the original met.
Syntax
map.keys()
Parameters
NONE
Return Value
Type
Description
Iterator An iterable object with the keys of the map.
Objects as Keys
Note
Being able to use objects as keys is an important map feature.
Example
// Create Objects
const apples = {name: 'Apples'};
const bananas = {name: 'Bananas'};
const oranges = {name: 'Oranges'};
// Create a Map
const fruits = new Map();
// Add new Elements to the Map
fruits.set(apples, 500);
fruits.set(bananas, 300);
fruits.set(oranges, 200);
Try it Yourself »
const apples = {name: 'Apples'};
const bananas = {name: 'Bananas'};
const oranges = {name: 'Oranges'};
// Create a Map
const fruits = new Map();
// Add new Elements to the Map
fruits.set(apples, 500);
fruits.set(bananas, 300);
fruits.set(oranges, 200);
Remember: The key is an object (apples), not a string ("apples"):
Browser Support
map.keys() is an ECMAScript6 (ES6 2015) feature.
JavaScript 2015 is supported in all browsers since June 2017:
| Chrome 51 |
Edge 15 |
Firefox 54 |
Safari 10 |
Opera 38 |
| May 2016 | Apr 2017 | Jun 2017 | Sep 2016 | Jun 2016 |