JavaScript Maps
The Map Object
A Map object holds key-value pairs where the keys can be any datatype.
A Map also remembers the original insertion order of the keys.
How to Create a Map
You can create a JavaScript Map by:
- Passing an Array to
new Map() - Create a Map and use
Map.set()
The new Map() Method
You can create a Map by passing an Array to the new Map() constructor:
Example
// Create a Map
const fruits = new Map([
["apples", 500],
["bananas", 300],
["oranges", 200]
]);
Try it Yourself »
The set() Method
You can add elements to a Map with the set() method:
Example
// Create a Map
const fruits = new Map();
// Set Map Values
fruits.set("apples", 500);
fruits.set("bananas", 300);
fruits.set("oranges", 200);
Try it Yourself »
The set() method can also be used to change existing Map values:
The get() Method
The get() method gets the value of a key in a Map:
Maps are Objects
typeof returns object:
instanceof Map returns true:
JavaScript Objects vs Maps
Differences between JavaScript Objects and Maps:
| Object | Map |
|---|---|
| Not directly iterable | Directly iterable |
| Do not have a size property | Have a size property |
| Keys must be Strings (or Symbols) | Keys can be any datatype |
| Keys are not well ordered | Keys are ordered by insertion |
| Have default keys | Do not have default keys |
Browser Support
Map is an ES6 feature.
ES6 is fully supported in all modern browsers since June 2017:
| Chrome 51 |
Edge 15 |
Firefox 54 |
Safari 10 |
Opera 38 |
| May 2016 | Apr 2017 | Jun 2017 | Sep 2016 | Jun 2016 |
