How to know if two arrays have the same values

Question

I have these two arrays  one is filled with information from an ajax request and another stores the buttons the user clicks on  I use this code  I filled with sample numbers    var array1    2  4   var array2    4  2     It cames from the user button clicks  so it might be disordered  array1 sort      Sorts both Ajax and user info  array2 sort    if  array1  array2        doSomething     else      doAnotherThing        But it always gives false  even if the two arrays are the same  but with different name   I checked this in Chrome s JS Console   So  is there any way I could know if these two arrays contain the same  Why is it giving false  How can I know which values in the first array are not in the second

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If you want to check only if two arrays have same values (regardless the number of occurrences and order of each value) you could do this by using lodash:

_.isEmpty(_.xor(array1, array2))

Short, simple and pretty!

User · Answer

Simple solution for shallow equality using ES6   const arr1test   arr1 slice   sort   const arr2test   arr2 slice   sort   const equal    arr1test some  val  idx    gt  val     arr2test idx      Creates shallow copies of each array and sorts them  Then uses some   to loop through arr1test values  checking each value against the value in arr2test with the same index  If all values are equal  some   returns false  and in turn equal evaluates to true   Could also use every    but it would have to cycle through every element in the array to satisfy a true result  whereas some   will bail as soon as it finds a value that is not equal   const equal   arr1test every  val  idx    gt  val     arr2test idx

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kindly check this answer  var arr1   12 18   var arr2   12  18  20  11  19  14  6  7  8  16  9  3  1  13  5  4  15  10  2  17   for i 0 i lt arr1 length i      var array1 arr1 i   for j 0 j lt arr2 length j          var array2 arr2 j       if array1  array2        return true

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I had simple integer values in a Game project Had less number of values in each array  also  needed that original array untouched So  I did the below  it worked fine   Code edited to paste here   var sourceArray    1  2  3   var targetArray    3  2  1    if  sourceArray length     targetArray length           not equal        did something     return false     var newSortedSourceArray   sourceArray slice   sort    var newSortedTargetArray   targetArray slice   sort     if  newSortedSourceArray toString       newSortedTargetArray toString         MAIN CHECK        not equal        did something     return false    else          equal        did something        continued further below       did some more work  return true    Hope that helps

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Using ES6  We ll use Ramda s equals function  but instead we can use Lodash s or Underscore s isEqual   const R   require  ramda     const arraysHaveSameValues    arr1  arr2    gt  R equals      arr1  sort        arr2  sort       Using the spread opporator  we avoid mutating the original arrays  and we keep our function pure

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Our aim is basically to check whether 2 arrays are equal sets  set is the mathematically defined set  Fastest sorting asymptotically takes O nlog n   time  So If you sort an array  it would take at least O nlog n   time  But you can do this task faster  which asymptotically takes O n  time  average case not worst case  with a dictionary data structure  In JS  a dictionary is simply an object with keys and values       assumes array elements are primitive types   check whether 2 arrays are equal sets     param     a1 is an array    param     a2 is an array    function areArraysEqualSets a1  a2      const superSet         for  const i of a1        const e   i   typeof i      superSet e    1         for  const i of a2        const e   i   typeof i      if   superSet e           return false            superSet e    2         for  let e in superSet        if  superSet e      1          return false               return true      Note that this function works with arrays of primitive types and assumes a1 and a2 are arrays

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Simple Solution to compare the two arrays   var array1    2  4   var array2    4  2    array1 sort    array2 sort     if  array1 0     array2 0         console log  Success     else      console log  Wrong

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What about this  ES 2017 i suppose    x000D   x000D  const array1    1  3  5   x000D  const array2    1  5  3   x000D   x000D  const isEqual    array1 length     array2 length   amp  amp   array1 every val   gt  array2 includes val     x000D  console log isEqual   x000D   x000D   x000D    1st condition checks if both arrays have same length and 2nd condition checks if 1st array is a subset of the 2nd array  Combining these 2 conditions should then result in comparison of all items of the 2 arrays irrespective of the ordering of elements   The above code will only work if both arrays have non-duplicate items

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Try this function arraysEqual arr1  arr2       if   Array isArray arr1      Array isArray arr2     arr1 length  arr2 length          return false       return arr1 length  arr1 filter word   gt  arr2 includes word   length

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If you want to compare two arrays and check if any object is same in both arrays it will works  Example    Array1    a b c d  Array2    d e f g   Here   d  is common in both array so this function will return true value      cehckArray array1  array2        for  let i   0  i  lt  array1 length  i            for  let j   0  j  lt  array2 length  j              if  array1 i      array2 j               return true                                 Return if no common element exist      return false

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You can use reduce instead of loops to appear clever  but at the risk of having your fellow developers think of you as a smart-ass   function isArrayContentSame a  b      if  Array isArray a   amp  amp  Array isArray b   amp  amp  a length    b length        a   a concat   sort       b   b concat   sort       return a reduce  acc e i    gt  acc  amp  amp  e     b i   true      else       return false

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Array prototype compare   function testArr        if  this length    testArr length  return false      for  var i   0  i  lt  testArr length  i              if  this i  compare      To test values in nested arrays             if   this i  compare testArr i    return false                    else if  this i      testArr i   return false            return true     var array1    2  4   var array2    4  2   if array1 sort   compare array2 sort           doSomething      else       doAnotherThing        Maybe

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Answering after long time but hope this will help somebody who looking for a simple solution and modern newbies   Now we can achieve this using multiple libraries like lodash  underscore  etc   These becomes part of the project nowadays due to simplicity  multiple features and high usage   You can use intersection from lodash library     intersection   2-1    1      2-2    3-1    2-1           gt    2-1     This will work for any data type

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Sort the arrays and compare their values one by one  function arrayCompare  arr1   arr2        if          Array isArray  arr1            Array isArray  arr2            arr1 length      arr2 length                   return false                       concat   to not mutate arguments     const arr1    arr1 concat   sort        const arr2    arr2 concat   sort             for  let i   0  i  lt  arr1 length  i              if  arr1 i      arr2 i                 return false                            return true

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You didn t seem to care about perf  not sure any of the other answer did either  Here s some benchmarks for both sameArrayMembers  ie   1 2 2      1 1 2   as well as sameArrayMembersAsSet  ie   1 2 2      1 1 2   Didn t check for  1 1 2  same as  1 2  which I probably should given if you re claiming to check for sets than you shouldn t have the length check   x000D   x000D  const tests        Maciej Krawczyk     arr1   arr2    gt         if   Array isArray  arr1       Array isArray  arr2      arr1 length      arr2 length        return false       var arr1    arr1 concat   sort        var arr2    arr2 concat   sort         for  var i   0  i  lt  arr1 length  i               if  arr1 i      arr2 i               return false              return true          canbax    a1  a2    gt        const superSet           for  const i of a1          const e   i   typeof i        superSet e    1             for  const i of a2          const e   i   typeof i        if   superSet e             return false                superSet e    2             for  let e in superSet          if  superSet e      1            return false                     return true          kennebec    array1  array2    gt        return array1 slice   sort   join         array2 slice   sort   join               Max Heiber   function         const containsAll    arr1  arr2    gt           arr2 every arr2Item   gt  arr1 includes arr2Item        return  arr1  arr2    gt           containsAll arr1  arr2   amp  amp  containsAll arr2  arr1             gman    a  b    gt        if  a length     b length    return false        const counts   new Map        for  const v of a          const count   counts get v     0        counts set v  count   1             for  const v of b          const count   counts get v         if   count         undefined or 0  both mean arrays are not the same         return false                counts set v  count - 1             return true          Bemmu    a  b    gt        if  Array isArray a   amp  amp  Array isArray b   amp  amp  a length    b length          a   a concat   sort         b   b concat   sort         return a reduce  acc e i    gt  acc  amp  amp  e     b i   true        else         return false                Sandeep    array1  array2    gt        return JSON stringify array1 sort        JSON stringify array2 sort             camslice    arr1  arr2    gt        const arr1test   arr1 slice   sort        const arr2test   arr2 slice   sort        return  arr1test some  val  idx    gt  val     arr2test idx            Dimitrios Stefos    arr1  arr2    gt        if   Array isArray arr1      Array isArray arr2     arr1 length  arr2 length          return false       return arr1 length  arr1 filter word   gt  arr2 includes word   length          SC1000    arr1  arr2  opts    gt        function vKey i  v          return  opts  enforceOrder      i -             typeof v -  v              if  arr1 length     arr2 length  return false       const d1           const d2             for  let i   arr1 length - 1  i  gt   0  i--          d1 vKey i  arr1 i      true        d2 vKey i  arr2 i      true             for  let i   arr1 length - 1  i  gt   0  i--          const v   vKey i  arr1 i          if  d1 v      d2 v   return false             for  let i   arr2 length - 1  i  gt   0  i--          const v   vKey i  arr2 i          if  d1 v      d2 v   return false             return true         Magnus Fohlstr  m    arr1  arr2    gt            let count    arr  val    gt  arr reduce  count  curr    gt   curr     val   1 0    count  0           return arr1 length     arr2 length  amp  amp  arr1 reduce  checks  val    gt              checks concat count arr1  val      count arr2  val        every check   gt  check                ----------------------------  function createExposedPromise      const p        p promise   new Promise  resolve  reject    gt       p resolve   resolve     p reject   reject        return p     function assert cond      if   cond        log  assert        throw new Error           async function main       await testResults true   sameArrayMembers      await testResults false   sameArrayMemembersAsSet         async function testResults asSet  msg        log   n           msg                        const suite   new Benchmark Suite        let test          reject if they fail simple test     const a    1 1 2       const b    1 2 2       for  const  name  fn  of Object entries tests           if  fn a  b      asSet            log    name  fails for   msg     a       b               else               suite add name       gt  test fn                       let endPromise       suite on  cycle   event   gt  log String event target         suite on  complete   function           log  Fastest is     this filter  fastest   map  name           endPromise resolve                 async function runWith num  title          log  ------    title    -----------           const a             for  let i   0  i  lt  num    i            a i    Math random                  const b       a         const c       a   c c length   2   0            endPromise   createExposedPromise           test    fn    gt            assert fn a  b           assert  fn a  c                    suite reset          suite run   async   true          await endPromise promise             await runWith 10   small  10         await runWith 100   medium  100         await runWith 10000   large  10000           main     function log    args      const elem   document createElement  pre      elem textContent   args join         document body appendChild elem     x000D  pre   margin  0    x000D   lt script src  https   unpkg com lodash 4 17 20 lodash js  gt  lt  script gt   lt script src  https   unpkg com benchmark 2 1 4 benchmark js  gt  lt  script gt  x000D   x000D   x000D   The results will probably change over time since JS engines get updated  Here s some results from 2020 09 28 Chrome 87          sameArrayMembers                canbax fails for sameArrayMembers  1 1 2    1 2 2   Max Heiber fails for sameArrayMembers  1 1 2    1 2 2   Dimitrios Stefos fails for sameArrayMembers  1 1 2    1 2 2   SC1000 fails for sameArrayMembers  1 1 2    1 2 2   ------  small  10    ----------- Maciej Krawczyk x 246 129 ops sec   0 84   66 runs sampled  kennebec x 182 234 ops sec   0 56   64 runs sampled  gman x 377 356 ops sec   1 55   64 runs sampled  Bemmu x 244 850 ops sec   0 76   64 runs sampled  Sandeep x 100 529 ops sec   1 53   63 runs sampled  camslice x 542 577 ops sec   0 68   64 runs sampled  Fastest is camslice ------  medium  100    ----------- Maciej Krawczyk x 12 121 ops sec   1 40   63 runs sampled  kennebec x 10 219 ops sec   1 60   63 runs sampled  gman x 41 225 ops sec   1 63   62 runs sampled  Bemmu x 12 400 ops sec   1 10   63 runs sampled  Sandeep x 12 470 ops sec   0 50   64 runs sampled  camslice x 57 126 ops sec   0 54   64 runs sampled  Fastest is camslice ------  large  10000    ----------- Maciej Krawczyk x 30 75 ops sec   0 86   42 runs sampled  kennebec x 27 35 ops sec   1 11   38 runs sampled  gman x 376 ops sec   0 46   62 runs sampled  Bemmu x 30 91 ops sec   0 77   42 runs sampled  Sandeep x 80 33 ops sec   0 54   53 runs sampled  camslice x 166 ops sec   0 44   61 runs sampled  Fastest is gman           sameArrayMemembersAsSet                Maciej Krawczyk fails for sameArrayMemembersAsSet  1 1 2    1 2 2   kennebec fails for sameArrayMemembersAsSet  1 1 2    1 2 2   gman fails for sameArrayMemembersAsSet  1 1 2    1 2 2   Bemmu fails for sameArrayMemembersAsSet  1 1 2    1 2 2   Sandeep fails for sameArrayMemembersAsSet  1 1 2    1 2 2   camslice fails for sameArrayMemembersAsSet  1 1 2    1 2 2   ------  small  10    ----------- canbax x 110 826 ops sec   2 07   63 runs sampled  Max Heiber x 2 699 807 ops sec   1 31   63 runs sampled  Dimitrios Stefos x 2 910 096 ops sec   0 65   62 runs sampled  SC1000 x 59 989 ops sec   2 61   63 runs sampled  Fastest is Dimitrios Stefos ------  medium  100    ----------- canbax x 9 624 ops sec   2 20   53 runs sampled  Max Heiber x 88 945 ops sec   0 71   64 runs sampled  Dimitrios Stefos x 94 425 ops sec   0 51   65 runs sampled  SC1000 x 5 742 ops sec   0 74   33 runs sampled  Fastest is Dimitrios Stefos ------  large  10000    ----------- canbax x 59 85 ops sec   1 69   46 runs sampled  Max Heiber x 13 50 ops sec   0 87   26 runs sampled  Dimitrios Stefos x 15 40 ops sec   0 89   30 runs sampled  SC1000 x 37 42 ops sec   1 47   40 runs sampled  Fastest is canbax  Firefox 80          sameArrayMembers                canbax fails for sameArrayMembers  1 1 2    1 2 2   Max Heiber fails for sameArrayMembers  1 1 2    1 2 2   Dimitrios Stefos fails for sameArrayMembers  1 1 2    1 2 2   SC1000 fails for sameArrayMembers  1 1 2    1 2 2   ------  small  10    ----------- Maciej Krawczyk x 118 391 ops sec   0 52   65 runs sampled  kennebec x 70 254 ops sec   0 40   67 runs sampled  gman x 201 659 ops sec   3 23   57 runs sampled  Bemmu x 118 133 ops sec   0 67   64 runs sampled  Sandeep x 69 484 ops sec   1 40   65 runs sampled  camslice x 130 443 ops sec   0 55   65 runs sampled  Fastest is gman ------  medium  100    ----------- Maciej Krawczyk x 11 418 ops sec   2 81   61 runs sampled  kennebec x 7 278 ops sec   1 37   41 runs sampled  gman x 19 748 ops sec   6 60   53 runs sampled  Bemmu x 11 535 ops sec   1 09   62 runs sampled  Sandeep x 8 234 ops sec   1 46   45 runs sampled  camslice x 14 277 ops sec   3 08   60 runs sampled  Fastest is gman ------  large  10000    ----------- Maciej Krawczyk x 65 25 ops sec   2 13   49 runs sampled  kennebec x 47 73 ops sec   0 82   51 runs sampled  gman x 210 ops sec   3 54   54 runs sampled  Bemmu x 66 90 ops sec   0 53   50 runs sampled  Sandeep x 63 13 ops sec   1 59   48 runs sampled  camslice x 115 ops sec   1 36   56 runs sampled  Fastest is gman           sameArrayMemembersAsSet                Maciej Krawczyk fails for sameArrayMemembersAsSet  1 1 2    1 2 2   kennebec fails for sameArrayMemembersAsSet  1 1 2    1 2 2   gman fails for sameArrayMemembersAsSet  1 1 2    1 2 2   Bemmu fails for sameArrayMemembersAsSet  1 1 2    1 2 2   Sandeep fails for sameArrayMemembersAsSet  1 1 2    1 2 2   camslice fails for sameArrayMemembersAsSet  1 1 2    1 2 2   ------  small  10    ----------- canbax x 79 433 ops sec   1 11   57 runs sampled  Max Heiber x 1 822 200 ops sec   0 92   65 runs sampled  Dimitrios Stefos x 2 258 820 ops sec   0 48   65 runs sampled  SC1000 x 35 784 ops sec   1 42   63 runs sampled  Fastest is Dimitrios Stefos ------  medium  100    ----------- canbax x 6 726 ops sec   0 60   38 runs sampled  Max Heiber x 41 620 ops sec   1 08   65 runs sampled  Dimitrios Stefos x 53 041 ops sec   1 61   64 runs sampled  SC1000 x 3 450 ops sec   0 56   64 runs sampled  Fastest is Dimitrios Stefos ------  large  10000    ----------- canbax x 44 18 ops sec   5 87   42 runs sampled  Max Heiber x 5 62 ops sec   4 79   19 runs sampled  Dimitrios Stefos x 6 77 ops sec   1 21   21 runs sampled  SC1000 x 24 18 ops sec   3 50   36 runs sampled  Fastest is canbax  Safari 14          sameArrayMembers                canbax fails for sameArrayMembers  1 1 2    1 2 2   Max Heiber fails for sameArrayMembers  1 1 2    1 2 2   Dimitrios Stefos fails for sameArrayMembers  1 1 2    1 2 2   SC1000 fails for sameArrayMembers  1 1 2    1 2 2   ------  small  10    ----------- Maciej Krawczyk x 142 798 ops sec   0 50   65 runs sampled  kennebec x 118 073 ops sec   1 12   63 runs sampled  gman x 760 109 ops sec   0 46   66 runs sampled  Bemmu x 136 265 ops sec   0 48   63 runs sampled  Sandeep x 69 868 ops sec   0 44   64 runs sampled  camslice x 155 548 ops sec   0 45   64 runs sampled  Fastest is gman ------  medium  100    ----------- Maciej Krawczyk x 8 479 ops sec   0 52   46 runs sampled  kennebec x 5 992 ops sec   2 54   34 runs sampled  gman x 83 390 ops sec   0 37   64 runs sampled  Bemmu x 8 615 ops sec   0 56   63 runs sampled  Sandeep x 5 943 ops sec   0 67   64 runs sampled  camslice x 8 753 ops sec   0 45   47 runs sampled  Fastest is gman ------  large  10000    ----------- Maciej Krawczyk x 62 66 ops sec   0 87   51 runs sampled  kennebec x 46 46 ops sec   0 66   48 runs sampled  gman x 615 ops sec   2 33   60 runs sampled  Bemmu x 60 98 ops sec   1 28   52 runs sampled  Sandeep x 49 11 ops sec   2 07   47 runs sampled  camslice x 66 33 ops sec   4 44   50 runs sampled  Fastest is gman           sameArrayMemembersAsSet                Maciej Krawczyk fails for sameArrayMemembersAsSet  1 1 2    1 2 2   kennebec fails for sameArrayMemembersAsSet  1 1 2    1 2 2   gman fails for sameArrayMemembersAsSet  1 1 2    1 2 2   Bemmu fails for sameArrayMemembersAsSet  1 1 2    1 2 2   Sandeep fails for sameArrayMemembersAsSet  1 1 2    1 2 2   camslice fails for sameArrayMemembersAsSet  1 1 2    1 2 2   ------  small  10    ----------- canbax x 167 041 ops sec   0 63   64 runs sampled  Max Heiber x 1 281 054 ops sec   0 74   59 runs sampled  Dimitrios Stefos x 1 127 639 ops sec   0 98   64 runs sampled  SC1000 x 112 824 ops sec   0 37   64 runs sampled  Fastest is Max Heiber ------  medium  100    ----------- canbax x 8 784 ops sec   0 53   47 runs sampled  Max Heiber x 37 824 ops sec   0 52   65 runs sampled  Dimitrios Stefos x 41 238 ops sec   0 85   63 runs sampled  SC1000 x 6 181 ops sec   0 61   35 runs sampled  Fastest is Dimitrios Stefos ------  large  10000    ----------- canbax x 63 83 ops sec   2 46   49 runs sampled  Max Heiber x 5 41 ops sec   0 52   18 runs sampled  Dimitrios Stefos x 6 02 ops sec   1 32   19 runs sampled  SC1000 x 42 25 ops sec   1 45   45 runs sampled  Fastest is canbax

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Most of the other solutions use sort  O n log n   use libraries or have O n 2  complexity  Here is a pure Javascript solution with linear complexity  O n          Check if two arrays of strings or numbers have the same values     param  string   number    arr1     param  string   number    arr2     param  Object   opts      param  boolean   opts enforceOrder  - By default  false   the order of the values in the arrays doesn t matter      return  boolean      function compareArrays arr1  arr2  opts       function vKey i  v        return  opts  enforceOrder      i -             typeof v -  v          if  arr1 length     arr2 length  return false     const d1         const d2           for  let i   arr1 length - 1  i  gt   0  i--        d1 vKey i  arr1 i      true      d2 vKey i  arr2 i      true           for  let i   arr1 length - 1  i  gt   0  i--        const v   vKey i  arr1 i        if  d1 v      d2 v   return false         for  let i   arr2 length - 1  i  gt   0  i--        const v   vKey i  arr2 i        if  d1 v      d2 v   return false         return true    Tests  arr1   1  2  arr2   1  2  compareArrays arr1  arr2    gt  true compareArrays arr1  arr2   enforceOrder  true     gt  true ------- arr1   1  2  arr2   2  1  compareArrays arr1  arr2    gt  true compareArrays arr1  arr2   enforceOrder  true     gt  false ------- arr1   2  1  arr2   1  2  compareArrays arr1  arr2    gt  true compareArrays arr1  arr2   enforceOrder  true     gt  false ------- arr1   2  2  arr2   1  2  compareArrays arr1  arr2    gt  false compareArrays arr1  arr2   enforceOrder  true     gt  false ------- arr1   1  2  arr2   1  2  3  compareArrays arr1  arr2    gt  false compareArrays arr1  arr2   enforceOrder  true     gt  false ------- arr1    quot 1 quot   arr2   1  compareArrays arr1  arr2    gt  false compareArrays arr1  arr2   enforceOrder  true     gt  false ------- arr1    quot 1 quot   2  arr2   2   quot 1 quot   compareArrays arr1  arr2    gt  true compareArrays arr1  arr2   enforceOrder  true     gt  false ------- arr1     arr2     compareArrays arr1  arr2    gt  true compareArrays arr1  arr2   enforceOrder  true     gt  true

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If you are using the Prototype Framework  you can use the intersect method of an array to find out of they are the same  regardless of the order    var array1    1 2   var array2    2 1    if array1 intersect array2  length     array1 length        alert  arrays are the same

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I have another way based on the accepted answer  function compareArrays array1  array2         if            Array isArray array1              Array isArray array2             array1 length     array2 length       return false       var first   array1 sort   map value   gt   String value    join        var second   array2 sort   map value   gt   String value    join         return first    second   true   false

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Another one line solution  array1 concat array2  filter  item  index  currentArr    gt  currentArr lastIndexOf item     currentArr indexOf item   length    0   or     array1     array2  filter  item  index  currentArr    gt  currentArr lastIndexOf item     currentArr indexOf item   length    0

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Object equality check JSON stringify array1 sort        JSON stringify array2 sort     The above test also works with arrays of objects in which case use a sort function as documented in http   www w3schools com jsref jsref sort asp  Might suffice for small arrays with flat JSON schemas

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If you only want to test for primitive values  you can try  if JSON stringify arr1 sort        JSON stringify arr2 sort         console log  invalid

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If your array items are not objects- if they are numbers or strings  for example  you can compare their joined strings to see if they have the same members in any order-  var array1   10  6  19  16  14  15  2  9  5  3  4  13  8  7  1  12  18  11  20  17   var array2   12  18  20  11  19  14  6  7  8  16  9  3  1  13  5  4  15  10  2  17    if array1 sort   join         array2 sort   join            alert  same members      else alert  not a match

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A function to Compare two Arrays  to check if both has same elements  Even if they are out of order    It s good for simple arrays   String Number Boolean null NaN   I don t use  sort    it modifies the original array  Some say s its bad    Caution  This function is limited it can t compare Objects quot       quot  or functions within these Arrays  arrays it s self are Objects     let arraysHasSameElements    arr1  arr2    gt            let count                  returns counting of occurrences               arr  val    gt  arr reduce  count  curr    gt   curr     val   1   0    count  0               this will return true if lengths of the arrays is equal             then compare them            return arr1 length     arr2 length                 compare arr1 against arr2               amp  amp  arr1 reduce  checks  val    gt                       creating array of checking if a value has equal amount of occurrences                     in both arrays  then adds true  check                      checks concat count arr1  val      count arr2  val                            checking if each check is equal to true  then  every   returns true                   every check   gt  check              let arr1       -99 true NaN 21 null false  help  -99  help  NaN            arr2    null -99    NaN NaN false true -99  help  21  help        arraysHasSameElements arr1  arr2     true      let arr3    false false false false false false            arr4    false false false false false false      arraysHasSameElements arr3  arr4     true          here we have uncommented version      let arraysHasSameElements    arr1  arr2    gt            let count    arr  val    gt  arr reduce  count  curr    gt   curr     val   1 0    count  0           return arr1 length     arr2 length  amp  amp  arr1 reduce  checks  val    gt              checks concat count arr1  val      count arr2  val        every check   gt  check

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When you compare those two arrays  you re comparing the objects that represent the arrays  not the contents     You ll have to use a function to compare the two   You could write your own that simply loops though one and compares it to the other after you check that the lengths are the same

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Why your code didn t work  JavaScript has primitive data types and non-primitive data types   For primitive data types     and     check whether the things on either side of the bars have the same value  That s why 1     1 is true    For non-primitive data types like arrays     and     check for reference equality  That is  they check whether arr1 and arr2 are the same object  In your example  the two arrays have the same objects in the same order  but are not equivalent   Solutions  Two arrays  arr1 and arr2  have the same members if and only if    Everything in arr2 is in arr1   AND   Everything in arr1 is in arr2   So this will do the trick  ES2016    const containsAll    arr1  arr2    gt                   arr2 every arr2Item   gt  arr1 includes arr2Item    const sameMembers    arr1  arr2    gt                           containsAll arr1  arr2   amp  amp  containsAll arr2  arr1    sameMembers arr1  arr2       true    This second solution using Underscore is closer to what you were trying to do   arr1 sort    arr2 sort       isEqual arr1  arr2       true    It works because isEqual checks for  deep equality   meaning it looks at more than just reference equality and compares values   A solution to your third question  You also asked how to find out which things in arr1 are not contained in arr2   This will do it  ES2015    const arr1    1  2  3  4   const arr2    3  2  1    arr1 filter arr1Item   gt   arr2 includes arr1Item         4     You could also use Underscore s difference  method     difference arr1  arr2        4     UPDATE  See  Redu s comment   my solution is for sameMembers  but what you may have in mind is sameMembersInOrder also-known-as deepEquals   UPDATE 2  If you don t care about the order of the members of the arrays  ES2015  s Set may be a better data structure than Array  See the MDN notes on how to implement isSuperset and difference using dangerous monkey-patching

[javascript] How to know if two arrays have the same values

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