The size accessor property returns the number of elements in a Map object.
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.
size
var myMap = new Map();
myMap.set('a', 'alpha');
myMap.set('b', 'beta');
myMap.set('g', 'gamma');
myMap.size // 3
| Specification | Status | Comment |
|---|---|---|
| ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Map.prototype.size' in that specification. | Standard | Initial definition. |
| ECMAScript Latest Draft (ECMA-262) The definition of 'Map.prototype.size' in that specification. | Draft |
| Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
| Basic support | 38 | 12 | 191 | 11 | 25 | 8 |
| Feature | Android webview | Chrome for Android | Edge mobile | Firefox for Android | Opera Android | iOS Safari | Samsung Internet |
|---|---|---|---|---|---|---|---|
| Basic support | 38 | 38 | 12 | 191 | 25 | 8 | ? |
1. From Firefox 13 to Firefox 18, 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.
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/size