The JavaScript Map object’s size property returns the number of key/value pairs in the map. It provides an efficient way to determine the count without the need to iterate over the entire map.
It’s useful for things like:
- Validating the number of entries before performing operations.
- Checking map capacity against thresholds.
- Implementing logic that depends on the count of items in the map.
The size property of a Map object in JavaScript is read-only and reflects the number of elements in a Map. It’s a straightforward way to get the count of entries, where each entry is a key-value pair.
How to use the size property
To access the size property, you simply reference it on your Map instance. Here’s an example:
let myMap = new Map();
myMap.set('key1', 'value1');
myMap.set('key2', 'value2');
console.log(myMap.size); // Outputs: 2
Size vs length
Unlike arrays, where you use length to get the number of elements, for a Map you must use size. This is because Map objects maintain the insertion order of elements and are a part of the ES6 specification.
How to Check if a Map is empty
You can check if a Map is empty by comparing its size property to 0:
if(myMap.size === 0) {
console.log('Map is empty');
}
Limitations and considerations
The size property is dynamic. If you add or remove items from the map, the size will update accordingly. Keep in mind that size is a property, not a method, so you do not call it with parentheses.