Deleting Objects in JavaScript

Question

I m a bit confused with JavaScript s delete operator  Take the following piece of code   var obj         helloText   Hello World       var foo   obj   delete obj    After this piece of code has been executed  obj is null  but foo still refers to an object exactly like obj  I m guessing this object is the same object that foo pointed to   This confuses me  because I expected that writing delete obj deleted the object that obj was pointing to in memory   not just the variable obj   Is this because JavaScript s Garbage Collector is working on a retain release basis  so that if I didn t have any other variables pointing to the object  it would be removed from memory    By the way  my testing was done in Safari 4

User · Answer

Just found a jsperf you may consider interesting in light of this matter. (it could be handy to keep it around to complete the picture)

It compares delete, setting null and setting undefined.

But keep in mind that it tests the case when you delete/set property many times.

User · Answer

Setting a variable to null makes sure to break any references to objects in all browsers including circular references being made between the DOM elements and Javascript scopes  By using delete command we are marking objects to be cleared on the next run of the Garbage collection  but if there are multiple variables referencing the same object  deleting a single variable WILL NOT free the object  it will just remove the linkage between that variable and the object  And on the next run of the Garbage collection  only the variable will be cleaned

User · Answer

variables declared implicitly  are properties of the global object  so delete works on them like it works on any property   Variables declared with var are indestructible

User · Answer

This work for me  although its not a good practice  It  simply delete all the  the associated element with which the object belong     for  element in homeService              delete homeService element

User · Answer

Aside from the GC questions  for performance one should consider the optimizations that the browser may be doing in the background -   http   coding smashingmagazine com 2012 11 05 writing-fast-memory-efficient-javascript   It appears it may be better to null the reference than to delete it as that may change the behind-the-scenes  class  Chrome uses

User · Answer

Coming from the Mozilla Documentation   You can use the delete operator to delete variables declared implicitly but not those declared with the var statement     Here is the link  https   developer mozilla org En Core JavaScript 1 5 Reference Operators Special Operators delete Operator

User · Answer

I stumbled across this article in my search for this same answer   What I ended up doing is just popping out obj pop   all the stored values objects in my object so I could reuse the object   Not sure if this is bad practice or not   This technique came in handy for me testing my code in Chrome Dev tools or FireFox Web Console

User · Answer

delete is not used for deleting an object in java Script    delete used for removing an object key in your case  var obj     helloText   Hello World       var foo   obj  delete obj    object is not deleted check obj still take same values  delete usage   delete obj helloText   and then check obj  foo  both are empty object

User · Answer

IE 5 through 8 has a bug where using delete on properties of a host object  Window  Global  DOM etc  throws TypeError  object does not support this action    var el document getElementById  anElementId    el foo    bar  baz    try      delete el foo   catch          alert  Curses  drats and double double damn         el foo undefined     a work around     Later if you need to check where the property has a meaning full value use el foo     undefined because  foo  in el  will always return true in IE   If you really need the property to really disappear     function hostProxy host       if host   null    host   undefined  return host      if    hostProxy  in host          host  hostproxy   host host prototype host             return host  hostproxy    var el hostProxy document getElementById  anElementId     el foo    bar  baz     delete el foo     removing property if a non-host object   if your need to use the host object with host api     el parent removeChild el  host

User · Answer

The delete command has no effect on regular variables  only properties  After the delete command the property doesn t have the value null  it doesn t exist at all   If the property is an object reference  the delete command deletes the property but not the object  The garbage collector will take care of the object if it has no other references to it   Example   var x   new Object    x y   42   alert x y      shows  42   delete x     no effect alert x y      still shows  42   delete x y     deletes the property alert x y      shows  undefined     Tested in Firefox

User · Answer

The delete operator deletes only a reference  never an object itself  If it did delete the object itself  other remaining references would be dangling  like a C   delete   And accessing one of them would cause a crash  To make them all turn null would mean having extra work when deleting or extra memory for each object    Since Javascript is garbage collected  you don t need to delete objects themselves - they will be removed when there is no way to refer to them anymore    It can be useful to delete references to an object if you are finished with them  because this gives the garbage collector more information about what is able to be reclaimed  If references remain to a large object  this can cause it to be unreclaimed - even if the rest of your program doesn t actually use that object

[javascript] Deleting Objects in JavaScript

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