unction: 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 

#  WeakSet

A **` WeakSet ` ** is a collection of garbage-collectable values, including
objects and [ non-registered symbols ](/en-
US/docs/Web/JavaScript/Reference/Global_Objects/Symbol#shared_symbols_in_the_global_symbol_registry)
. A value in the ` WeakSet ` may only occur once. It is unique in the `
WeakSet ` 's collection.

##  Description

Values of WeakSets must be garbage-collectable. Most [ primitive data types
](/en-US/docs/Glossary/Primitive) can be arbitrarily created and don't have a
lifetime, so they cannot be stored. Objects and [ non-registered symbols
](/en-
US/docs/Web/JavaScript/Reference/Global_Objects/Symbol#shared_symbols_in_the_global_symbol_registry)
can be stored because they are garbage-collectable.

The main differences to the [ ` Set ` ](/en-
US/docs/Web/JavaScript/Reference/Global_Objects/Set) object are:

  * ` WeakSet ` s are collections of **objects and symbols only** . They cannot contain arbitrary values of any type, as [ ` Set ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) s can. 
  * The ` WeakSet ` is _weak_ , meaning references to objects in a ` WeakSet ` are held _weakly_ . If no other references to a value sto