-US/docs/Web/JavaScript/Reference/Global_Objects/Function/caller) Non-standard  Deprecated 
    3. [ ` Function: displayName ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/displayName) Non-standard 
    4. [ ` Function: length ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length)
    5. [ ` Function: name ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name)
    6. [ ` Function: prototype ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/prototype)
  9. Methods 
    1. [ ` Function.prototype[@@hasInstance]() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/@@hasInstance)
    2. [ ` Function.prototype.apply() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/apply)
    3. [ ` Function.prototype.bind() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind)
    4. [ ` Function.prototype.call() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call)
    5. [ ` Function.prototype.toString() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/toString)
  10. [ ` Object ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object)
  11. Properties 
    1. [ ` Object.prototype.constructor ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor)
    2. [ ` Object.prototype.__proto__ ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/proto) Deprecated 
  12. Methods 
    1. [ ` Object.prototype.__defineGetter__() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/__defineGetter__) Deprecated 
    2. [ ` Object.prototype.__defineSetter__() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/__defineSetter__) Deprecated 
    3. [ ` Object.prototype.__lookupGetter__() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/__lookupGetter__) Deprecated 
    4. [ ` Object.prototype.__lookupSetter__() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/__lookupSetter__) Deprecated 
    5. [ ` Object.prototype.hasOwnProperty() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty)
    6. [ ` Object.prototype.isPrototypeOf() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isPrototypeOf)
    7. [ ` Object.prototype.propertyIsEnumerable() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/propertyIsEnumerable)
    8. [ ` Object.prototype.toLocaleString() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/toLocaleString)
    9. [ ` Object.prototype.toString() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/toString)
    10. [ ` Object.prototype.valueOf() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/valueOf)

##  In this article

  * Description 
  * Constructor 
  * Instance properties 
  * Instance methods 
  * Examples 
  * Specifications 
  * Browser compatibility 
  * See also 

#  WeakMap

A **` WeakMap ` ** is a collection of key/value pairs whose keys must be
objects or [ non-registered symbols ](/en-
US/docs/Web/JavaScript/Reference/Global_Objects/Symbol#shared_symbols_in_the_global_symbol_registry)
, with values of any arbitrary [ JavaScript type ](/en-
US/docs/Web/JavaScript/Data_structures) , and which does not create strong
references to its keys. That is, an object's presence as a key in a ` WeakMap
` does not prevent the object from being garbage collected. Once an object
used as a key has been collected, its corresponding values in any ` WeakMap `
become candidates for garbage collection as well â as long as they aren't
strongly referred to elsewhere. The only primitive type that can be used as a
` WeakMap ` key is symbol â more specifically, [ non-registered symbols
](/en-
US/docs/Web/JavaScript/Reference/Global_Objects/Symbol#shared_symbols_in_the_global_symbol_registry)
â because non-registered symbols are guaranteed to be unique and cannot be
re-created.

` WeakMap ` allows associating data to objects in a way that