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
Supported in the Internet Explorer 11 standards document mode. Also supported in Store apps (Windows 8.1 and Windows Phone 8.1). See Version Information.
Not supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards. Not supported in Windows 8.