WeakMap.prototype.has() - JavaScript 编辑

The has() method returns a boolean indicating whether an element with the specified key exists in the WeakMap object or not.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Syntax

ws.has(key);

Parameters

key

Required. The key of the element to test for presence in the WeakMap object.

Return value

Boolean

Returns true if an element with the specified key exists in the WeakMap object; otherwise false.

Examples

Using the has method

var wm = new WeakMap();
wm.set(window, 'foo');

wm.has(window); // returns true
wm.has('baz');  // returns false

Specifications

Specification
ECMAScript (ECMA-262) The definition of 'WeakMap.prototype.has' in that specification.

Browser compatibility

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See also

• WeakMap
• WeakMap.prototype.set()
• WeakMap.prototype.get()