How to quickly clear a JavaScript Object

Question

With a JavaScript Array  I can reset it to an empty state with a single assignment   array length   0    This makes the Array  appear  empty and ready to reuse  and as far as I understand is a single  operation  - that is  constant time   Is there a similar way to clear a JS Object  I know I can iterate its fields deleting them   for  var prop in obj    if  obj hasOwnProperty prop     delete obj prop         but this has linear complexity   I can also just throw the object away and create a new one   obj         But  promiscuous  creation of new objects leads to problems with Garbage Collection on IE6   As described here

User · Accepted Answer

The short answer to your question  I think  is no  you can just create a new object     In this example  I believe setting the length to 0 still leaves all of the elements for garbage collection  You could add this to Object prototype if it s something you d frequently use  Yes it s linear in complexity  but anything that doesn t do garbage collection later will be  This is the best solution  I know it s not related to your question - but for how long do we need to continue supporting IE6  There are many campaigns to discontinue the usage of it    Feel free to correct me if there s anything incorrect above

User · Answer

You can try this  Function below sets all values of object s properties to undefined  Works as well with nested objects   var clearObjectValues    objToClear    gt        Object keys objToClear  forEach  param    gt            if    objToClear param   toString         object Object                   clearObjectValues objToClear param              else               objToClear param    undefined                       return objToClear

User · Answer

Something new to think about looking forward to Object observe in ES7 and with data-binding in general  Consider   var foo      name   hello      Object observe foo  function   alert  modified          bind to foo  foo        You are no longer bound to foo but to an orphaned version of it foo name  there      This change will be missed by Object observe     So under that circumstance  2 can be the best choice

User · Answer

This bugged me for ages so here is my version as I didn t want an empty object  I wanted one with all the properties but reset to some default value  Kind of like a new instantiation of a class    x000D   x000D  let object1     x000D    a   somestring   x000D    b  42  x000D    c  true  x000D    d   x000D      e 1  x000D      f 2  x000D      g true  x000D      h   x000D        i  hello  x000D        x000D       x000D    j   1 2 3   x000D    k    foo    bar    x000D    l   foo  1 true   x000D    m   n 10  o  food   p true     n 11  o  foog   p true     x000D    q null  x000D    r undefined x000D     x000D   x000D  let boolDefault   false  x000D  let stringDefault       x000D  let numberDefault   0  x000D   x000D  console log object1   x000D    document write   lt pre gt     x000D    document write JSON stringify object1   x000D    document write   lt hr   gt     x000D  cleanObject object1   x000D  console log object1   x000D    document write JSON stringify object1    x000D    document write   lt  pre gt     x000D   x000D  function cleanObject o    x000D    for  let  key  value  of Object entries o     x000D      let propType   typeof o key    x000D   x000D        console log key  value  propType   x000D   x000D      switch  propType    x000D        case  number    x000D          o key    numberDefault  x000D          break  x000D   x000D        case  string   x000D          o key    stringDefault  x000D          break  x000D   x000D        case  boolean   x000D          o key    boolDefault      x000D          break  x000D   x000D        case  undefined   x000D          o key    undefined     x000D          break  x000D   x000D        default  x000D          if value     null    x000D              continue  x000D            x000D   x000D          cleanObject o key    x000D          break  x000D        x000D      x000D    x000D   x000D     EXPECTED OUTPUT x000D     Object   a   somestring   b  42  c  true  d  Object   e  1  f  2  g  true  h  Object   i   hello       j  Array  1  2  3   k  Array   foo    bar    l  Array   foo   1  true   m  Array  Object   n  10  o   food   p  true    Object   n  11  o   foog   p  true     q  null  r  undefined   x000D     Object   a      b  0  c  undefined  d  Object   e  0  f  0  g  undefined  h  Object   i          j  Array  0  0  0   k  Array           l  Array      0  undefined   m  Array  Object   n  0  o      p  undefined    Object   n  0  o      p  undefined     q  null  r  undefined   x000D   x000D   x000D

User · Answer

You can delete the props  but don t delete variables  delete abc  is invalid in ES5  and throws with use strict    You can assign it to null to set it for deletion to the GC  it won t if you have other references to properties   Setting length property on an object does not change anything   it only  well  sets the property

User · Answer

So to recap your question  you want to avoid  as much as possible  trouble with the IE6 GC bug   That bug has two causes    Garbage Collection occurs once every so many allocations  therefore  the more allocations you make  the oftener GC will run  The more objects you ve got    in the air     the more time each Garbage Collection run takes  since it ll crawl through the entire list of objects to see which are marked as garbage     The solution to cause 1 seems to be  keep the number of allocations down  assign new objects and strings as little as possible   The solution to cause 2 seems to be  keep the number of  live  objects down  delete your strings and objects as soon as you don t need them anymore  and create them afresh when necessary   To a certain extent  these solutions are contradictory  to keep the number of objects in memory low will entail more allocations and de-allocations   Conversely  constantly reusing the same objects could mean keeping more objects in memory than strictly necessary     Now for your question  Whether you ll reset an object by creating a new one  or by deleting all its properties  that will depend on what you want to do with it afterwards   You   ll probably want to assign new properties to it    If you do so immediately  then I suggest assigning the new properties straightaway  and skip deleting or clearing first   Make sure that all properties are either overwritten or deleted  though   If the object won t be used immediately  but will be repopulated at some later stage  then I suggest deleting it or assigning it null  and create a new one later on    There s no fast  easy to use way to clear a JScript object for reuse as if it were a new object     without creating a new one   Which means the short answer to your question is    No     like jthompson says

User · Answer

ES5  ES5 solution can be      for enumerable and non-enumerable properties Object getOwnPropertyNames obj  forEach function  prop      delete obj prop         ES6  And ES6 solution can be      for enumerable and non-enumerable properties for  const prop of Object getOwnPropertyNames obj       delete obj prop       Performance  Regardless of the specs  the quickest solutions will generally be      for enumerable and non-enumerable of an object with proto chain var props   Object getOwnPropertyNames obj   for  var i   0  i  lt  props length  i        delete obj props i          for enumerable properties of shallow plain object for  var key in obj         this check can be safely omitted in modern JS engines      if  obj hasOwnProperty key       delete obj key       The reason why for  in should be performed only on shallow or plain object is that it traverses the properties that are prototypically inherited  not just own properties that can be deleted  In case it isn t known for sure that an object is plain and properties are enumerable  for with Object getOwnPropertyNames is a better choice

User · Answer

Well  at the risk of making things too easy     for  var member in myObject  delete myObject member        would seem to be pretty effective in cleaning the object in one line of code with a minimum of scary brackets  All members will be truly deleted instead of left as garbage   Obviously if you want to delete the object itself  you ll still have to do a separate delete   for that

User · Answer

Assuming your object name is BASKET  simply set BASKET    quot  quot

[javascript] How to quickly clear a JavaScript Object?

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