How to determine if object is in array

Question

I need to determine if an object already exists in an array in javascript   eg  dummycode    var carBrands        var car1    name  ford    var car2    name  lexus    var car3    name  maserati    var car4    name  ford     carBrands push car1   carBrands push car2   carBrands push car3   carBrands push car4     now the  carBrands  array contains all instances   I m now looking a fast solution to check if an instance of car1  car2  car3 or car4 is already in the carBrands array   eg   var contains    carBrands Contains car1      lt --- returns bool    car1 and car4 contain the same data but are different instances they should be     tested as not equal   Do I have add something like a hash to the objects on creation  Or is there a faster way to do this in Javascript   I am looking for the fastest solution here  if dirty  so it has to be    In my app it has to deal with around 10000 instances   no jquery

User · Answer

I used underscore javascript library to tweak this issue   function containsObject obj  list     var res     find list  function val   return   isEqual obj  val      return    isObject res    true false      please refer to underscore js documentation for the underscore functions used in the above example   note  This is not a pure javascript solution  Shared for educational purposes

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Why don t you use the indexOf method of javascript arrays   Check this out  MDN indexOf Arrays  Simply do   carBrands indexOf car1     It will return you the index  position in the array  of car1  It will return -1 if car1 was not found in the array   http   jsfiddle net Fraximus r154cd9o  Edit  Note that in the question  the requirements are to check for the same object referenced in the array  and NOT a new object  Even if the new object is identical in content to the object in the array  it is still a different object  As mentioned in the comments  objects are passed by reference in JS and the same object can exist multiple times in multiple structures  If you want to create a new object and check if the array contains objects identical to your new one  this answer won t work  Julien s fiddle below   if you want to check for that same object s existence in the array  then this answer will work  Check out the fiddles here and in the comments

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I would use a generic iterator of property value over the array  No jQuery required   arr     prop1   val1   prop2   val2     prop1   val3   prop2   val4      objectPropInArray arr   prop1    val3        lt -- returns true  function objectPropInArray list  prop  val      if  list length  gt  0         for  i in list          if  list i  prop      val            return true                      return false

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You could use jQuery s grep method     grep carBrands  function obj    return obj name     ford         But as you specify no jQuery  you could just make a derivative of the function  From the source code   function grepArray  elems  callback  inv           var ret                 Go through the array  only saving the items          that pass the validator function       for   var i   0  length   elems length  i  lt  length  i                 if    inv      callback  elems  i    i                     ret push  elems  i                                 return ret         grepArray carBrands  function obj    return obj name     ford

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You can just use the equality operator      Objects are checked by reference by default  so you don t even need to use the     operator   try this  just make sure you re using the correct variable reference in the place of car1   var i  car  l   cars length   for  i   0  i  lt  l  i        if   car   cars i      car1          break        else car   null      Edit to add   An array extension was mentioned  so here s the code for it   Array prototype contains   Array prototype contains    function obj      var i  l   this length    for  i   0  i  lt  l  i            if  this i     obj  return true        return false       Note that I m caching the length value  as the Array s length property is actually an accessor  which is marginally slower than an internal variable

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i know this is an old post  but i wanted to provide a JQuery plugin version and my code      Find the first occurrence of object in list  Similar to   grep  but stops searching  function findFirst a b   var i  for  i   0  i  lt  a length    i    if  b a i   i   return a i     return undefined      usage   var product     findFirst arrProducts  function p    return p id    10

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This function is to check for a unique field  Arg 1  the array with selected data Arg 2  key to check Arg 3  value that must be  validated   function objectUnique  array  field  value         var unique   true      array forEach function   entry                 if   entry field     value                         unique   false                         return unique

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You could try sorting the array based on a property  like so   carBrands   carBrands sort function x y     return  x    y    0    x  gt  y    1   -1        Then you can use an iterative routine to check whether  carBrands Math floor carBrands length 2       change carBrands length to a var that keeps     getting divided by 2 until result is the target     or no valid target exists   is greater or lesser than the target  and so on  which will let you go through the array quickly to find whether the object exists or not

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try Array prototype some    MDN Array prototype some       function isBiggerThan10 element  index  array          return element  gt  10             2  5  8  1  4  some isBiggerThan10       false      12  5  8  1  4  some isBiggerThan10      true

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Use something like this   function containsObject obj  list        var i      for  i   0  i  lt  list length  i              if  list i      obj                return true                       return false      In this case  containsObject car4  carBrands  is true   Remove the carBrands push car4   call and it will return false instead   If you later expand to using objects to store these other car objects instead of using arrays  you could use something like this instead   function containsObject obj  list        var x      for  x in list            if  list hasOwnProperty x   amp  amp  list x      obj                return true                       return false      This approach will work for arrays too  but when used on arrays it will be a tad slower than the first option

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Having been recently bitten by the FP bug reading many wonderful accounts of how neatly the functional paradigm fits with Javascript   I replicate the code for completeness sake and suggest two ways this can be done functionally       var carBrands          var car1    name  ford      var car2    name  lexus      var car3    name  maserati      var car4    name  ford      var car5    name  toyota       carBrands push car1     carBrands push car2     carBrands push car3     carBrands push car4         ES6 approach which uses the includes method  Chrome47   Firefox43      carBrands includes car1     - gt  true   carBrands includes car5     - gt  false   If you need to support older browsers use the polyfill  it seems IE9  and Edge do NOT support it  Located in polyfill section of MSDN page  Alternatively I would like to propose an updated answer to cdhowie      ES2015 syntax function containsObject obj  list         return list some function elem          return elem     obj              or ES6  syntax with cool fat arrows function containsObject obj  list         return list some elem   gt  elem     obj

[javascript] How to determine if object is in array

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