W3cubDocs

map.size

The size accessor property returns the number of elements in a Map object.

Description

The value of size is an integer representing how many entries the Map object has. A set accessor function for size is undefined; you can not change this property.

Examples

Using `size`

var myMap = new Map();
myMap.set('a', 'alpha');
myMap.set('b', 'beta');
myMap.set('g', 'gamma');

myMap.size // 3

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Map.prototype.size' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of 'Map.prototype.size' in that specification.	Draft

Browser compatibility

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari
Basic support	38	19 (19)	11	25	7.1

Feature	Android	Chrome for Android	Firefox Mobile (Gecko)	IE Mobile	Opera Mobile	Safari Mobile
Basic support	No support	38	19.0 (19)	No support	No support	8

Gecko-specific notes

From Gecko 13 (Firefox 13 / Thunderbird 13 / SeaMonkey 2.10) to Gecko 18 (Firefox 18 / Thunderbird 18 / SeaMonkey 2.15 / Firefox OS 1.0.1 / Firefox OS 1.1) the size property was implemented as a Map.prototype.size() method, this has been changed to a property in later versions conform to the ECMAScript 2015 specification (bug 807001).