How to check JavaScript map size? [SOLVED]

Introduction

The Map object is a simple key/value map. Any value (objects and primitive values) may be used as either a key or a value. The Map object is a new object type introduced in JavaScript 1.6.

A Map is an associative array, meaning a set of key/value pairs. A key can be any value used as an index, including a string, number, or object. A value can be any JavaScript value (including another object).

In this article, we will talk about JavaScript Map objects and how to check a Map size.

 

Understanding JavaScript Map

We can create a Map with the new operator:

let myMap = new Map();

Or it can be created from an array of key/value pairs:

var myMap = new Map([
    ["key1", "value1"],
    ["key2", "value2"],
]);

Once a map is created, you can add, remove, and lookup key/value pairs with the following methods:

myMap.set("key", "value");
myMap.get("key");
myMap.has("key");
myMap.delete("key");

You can also iterate over the keys or values in a map with the following methods:

myMap.keys();
myMap.values();
myMap.entries();

Each method returns an iterator that can loop over the keys, values, or key/value pairs in the map. Here is a simple example that creates a map, adds some key/value pairs, and then iterates over the keys and values:

var myMap = new Map();

myMap.set("key1", "value1");
myMap.set("key2", "value2");

for (var key of myMap.keys()) {
    console.log(key);
}
for (var value of myMap.values()) {
    console.log(value);
}
for (var [key, value] of myMap.entries()) {
    console.log(key + " = " + value);
}

Output

key1
key2
value1
value2
key1 = value1
key2 = value2

Now that we understand about Maps, how to get the size of a JavaScript Map object.

 

Check JavaScript Map Size

To obtain a JavaScript Map size, we can make use of the size property. The return value is the number of elements present within the Map object.

Here is a code showing us how to check the size of a JavaScript Map

var myMap = new Map();

myMap.set("key1", "value1");
myMap.set("key2", "value2");
myMap.set("key3", "value3");

console.log(myMap.size);

Output

3

 

Summary

JavaScript Map object allows us to store key/value pairs, and to obtain their size, we can make use of the size property which returns the number of elements present within the Map object.

 

References

Map - JavaScript | MDN (mozilla.org)
Map.prototype.size - JavaScript | MDN (mozilla.org)