JavaScript WeakMap
JavaScript WeakMap is used to store a collection of key-value pairs that are weakly referenced which means if garbage collection is possible it would not be prevented. In a WeakMap the keys are strictly objects but values can be any primitive JavaScript Data Type. A WeakMap is not enumerable as the references are loose. WeakMaps are mainly used to store extra data where cleaning of memory does not affect the program much
Syntax:
new WeakMap() new WeakMap(iter)
Parameter: It has only one optional parameter.
- iter: It is an iterable JavaScript object that implements the @@iterator method. It contains two elements where the first is key and the second is value.
Example 1: In this example, we will construct a weakmap object and element, then check whether the element exists.
Javascript
function myBeginner() { let looseMap = new WeakMap(); let Ram = {name}; let Raj = {name}; let Rahul = {name}; looseMap.set(Ram, "Ram"); looseMap.set(Raj, "Raj"); looseMap.set(Rahul, "Rahul"); console.log(looseMap); console.log(looseMap.has(Ram))}myBeginner(); |
Output:
WeakMap {{…} => 'Raj', {…} => 'Rahul', {…} => 'Ram'}
true
Example 2: In this example, we will understand how garbage collection works in WeakMap.
Javascript
let looseMap = new WeakMap();let Ram = {name};looseMap.set(Ram, "Ram");console.log(looseMap);Ram = null;console.log(looseMap)setTimeout(function(){ console.log(looseMap);}, 300) |
Output: As the reference is removed from the memory so the value in looseMap are garbage collected
WeakMap {{…} => 'Ram'}
WeakMap {{…} => 'Ram'}
WeakMap {}
Supported Browsers:
- Google Chrome
- Internet Explorer
- Firefox
- Apple Safari
- Opera
We have a complete list of Javascript WeakMap methods, to check those please go through this JavaScript WeakMap Complete Reference article.