weakmap-object-javascript.md

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WeakMap Object (JavaScript) | Microsoft Docs		01/18/2017	windows-client-threshold			devlang-javascript		language-reference	WeakMap	JavaScript TypeScript DHTML	4682d2dc-caf9-4fa8-8313-a0a0b804fd1d	9	mikejo5000	mikejo	ghogen

WeakMap Object (JavaScript)

A collection of key/value pairs in which each key is an object reference.

Syntax

weakmapObj = new WeakMap()  

Remarks

A WeakMap object cannot be enumerated.

If you add a value to the collection using an existing key, the new value will replace the old value.

In a WeakMap object, references to key objects are held 'weakly'. This means that WeakMap will not prevent a garbage collection from happening on the key objects. When there are no references (other than WeakMap) to the key objects, the garbage collector may collect the key objects.

Properties

The following table lists the properties of the WeakMap object.

Property	Description
constructor	Specifies the function that creates a WeakMap.
prototype	Returns a reference to the prototype for a WeakMap.

Methods

The following table lists the methods of the WeakMap object.

Method	Description
clear	Removes all elements from a WeakMap.
delete	Removes a specified element from a WeakMap.
get	Returns a specified element from a WeakMap.
has	Returns true if the WeakMap contains a specified element.
set	Adds a new element to a WeakMap.
toString	Returns a string representation of a WeakMap.
valueOf	Returns the primitive value of the specified object.

Example

The following example shows how to add members to a WeakMap object and then retrieve them.

var dog = {  
    breed: "yorkie"  
}  
  
var cat = {  
    breed: "burmese"  
}  
  
var wm = new WeakMap();  
wm.set(dog, "fido");  
wm.set(cat, "pepper");  
  
document.write(wm.get(dog) + ": ");  
document.write(dog.breed);  
document.write("<br />");  
document.write(wm.get(cat) + ": ");  
document.write(cat.breed);  
  
// Output:  
// fido: yorkie  
// pepper: burmese  
  

Requirements

[!INCLUDEjsv11]