Map.prototype.size

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The size accessor property of Map instances returns the number of elements in this map.

Try it

const map = new Map();

map.set("a", "alpha");
map.set("b", "beta");
map.set("g", "gamma");

console.log(map.size);
// Expected output: 3

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

js
const myMap = new Map();
myMap.set("a", "alpha");
myMap.set("b", "beta");
myMap.set("g", "gamma");

console.log(myMap.size); // 3

Specifications

Specification

ECMAScript® 2027 Language Specification
# sec-get-map.prototype.size

Browser compatibility

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This page was last modified on Jul 20, 2025 by MDN contributors.

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Standard built-in objects
Map
Constructor
1. Map()
Static methods
1. groupBy()
Static properties
1. [Symbol.species]
Instance methods
Instance properties
1. size
Inheritance
Object/Function
Static methods
Static properties
Instance methods
Instance properties
1. __proto__
2. constructor