JavaScript Object Id

Question

Do JavaScript objects variables have some sort of unique identifier  Like Ruby has object id  I don t mean the DOM id attribute  but rather some sort of memory address of some kind

User · Accepted Answer

No  objects don t have a built in identifier  though you can add one by modifying the object prototype   Here s an example of how you might do that    function         var id   0       function generateId     return id            Object prototype id   function             var newId   generateId             this id   function     return newId              return newId                 That said  in general modifying the object prototype is considered very bad practice   I would instead recommend that you manually assign an id to objects as needed or use a touch function as others have suggested

User · Answer

Actually  you don t need to modify the object prototype  The following should work to  obtain  unique ids for any object  efficiently enough   var   next objid 1  function objectId obj        if  obj  null  return null      if  obj   obj id  null  obj   obj id   next objid        return obj   obj id

User · Answer

I ve just come across this  and thought I d add my thoughts  As others have suggested  I d recommend manually adding IDs  but if you really want something close to what you ve described  you could use this   var objectId    function          var allObjects            var f   function obj            if  allObjects indexOf obj      -1                allObjects push obj                     return allObjects indexOf obj             f clear   function           allObjects                  return f          You can get any object s ID by calling objectId obj   Then if you want the id to be a property of the object  you can either extend the prototype   Object prototype id   function          return objectId this       or you can manually add an ID to each object by adding a similar function as a method   The major caveat is that this will prevent the garbage collector from destroying objects when they drop out of scope    they will never drop out of the scope of the allObjects array  so you might find memory leaks are an issue  If your set on using this method  you should do so for debugging purpose only  When needed  you can do objectId clear   to clear the allObjects and let the GC do its job  but from that point the object ids will all be reset

User · Answer

If you want to lookup associate an object with a unique identifier without modifying the underlying object  you can use a WeakMap     Note that object must be an object or array     NOT a primitive value like string  number  etc  var objIdMap new WeakMap  objectCount   0  function objectId object     if   objIdMap has object   objIdMap set object   objectCount     return objIdMap get object      var o1     o2     o3  a 1   o4  a 1   console log  objectId o1       1 console log  objectId o2       2 console log  objectId o1       1 console log  objectId o3       3 console log  objectId o4       4 console log  objectId o3       3  Using a WeakMap instead of Map ensures that the objects can still be garbage-collected

[javascript] JavaScript Object Id

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