In Javascript how do I check if an array has duplicate values

Question

Possible Duplicate    Easiest way to find duplicate values in a javascript array       How do I check if an array has duplicate values   If some elements in the array are the same  then return true  Otherwise  return false     hello   goodbye   hey     return false because no duplicates exist   hello   goodbye   hello      return true because duplicates exist   Notice I don t care about finding the duplication  only want Boolean result whether arrays contains duplications

User · Answer

Well I did a bit of searching around the internet for you and I found this handy link.

Easiest way to find duplicate values in a JavaScript array

You can adapt the sample code that is provided in the above link, courtesy of "swilliams" to your solution.

User · Answer

If you have an ES2015 environment  as of this writing  io js  IE11  Chrome  Firefox  WebKit nightly   then the following will work  and will be fast  viz  O n     function hasDuplicates array        return  new Set array   size     array length        If you only need string values in the array  the following will work   function hasDuplicates array        var valuesSoFar   Object create null       for  var i   0  i  lt  array length    i            var value   array i           if  value in valuesSoFar                return true                    valuesSoFar value    true            return false      We use a  hash table  valuesSoFar whose keys are the values we ve seen in the array so far  We do a lookup using in to see if that value has been spotted already  if so  we bail out of the loop and return true     If you need a function that works for more than just string values  the following will work  but isn t as performant  it s O n2  instead of O n    function hasDuplicates array        var valuesSoFar           for  var i   0  i  lt  array length    i            var value   array i           if  valuesSoFar indexOf value      -1                return true                    valuesSoFar push value             return false      The difference is simply that we use an array instead of a hash table for valuesSoFar  since JavaScript  hash tables   i e  objects  only have string keys  This means we lose the O 1  lookup time of in  instead getting an O n  lookup time of indexOf

User · Answer

Another approach  also for object array elements within the array1  could be2   function chkDuplicates arr justCheck     var len   arr length  tmp       arrtmp   arr slice    dupes         arrtmp sort      while len--      var val   arrtmp len      if   nul nan infini i test String val          val   String val             if  tmp JSON stringify val            if  justCheck   return true          dupes push val             tmp JSON stringify val     true        return justCheck   false   dupes length   dupes   null      usages chkDuplicates  1 2 3 4 5  true                                 gt  false chkDuplicates  1 2 3 4 5 9 10 5 1 2  true                      gt  true chkDuplicates   a 1 b 2  1 2 3 4  a 1 b 2   1 2 3   true       gt  true chkDuplicates  null 1 2 3 4  a 1 b 2  NaN  true                gt  false chkDuplicates  1 2 3 4 5 1 2                                   gt   1 2  chkDuplicates  1 2 3 4 5                                       gt  null   See also     1 needs a browser that supports JSON  or a JSON library if not  2 edit  function can now be used for simple check or to return an array of duplicate values

[javascript] In Javascript, how do I check if an array has duplicate values?

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