Fastest JavaScript summation

Question

What is the fastest way to sum up an array in JavaScript  A quick search turns over a few different methods  but I would like a native solution if possible  This will run under SpiderMonkey    Thinking very inside-the-box I have been using   var count   0  for var i   0  i  lt  array length  i          count   count   array i       I m sure there is a better way then straight iteration

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I tried using performance now   to analyze the performance of the different types of loops  I took a very large array and found the sum of all elements of the array  I ran the code three times every time and found forEach and reduce to be a clear winner      For loop  let arr       Array 100000  keys    function addUsingForLoop ar     let sum   0    for let i   0  i  lt  ar length  i         sum    ar i          console log  Sum    sum        return sum    let t1   performance now    addUsingForLoop arr   let t2   performance now    console log  Time Taken      t2 - t1   milliseconds        Sum  4999950000      Time Taken   42 17500000959262 milliseconds      Sum  4999950000      Time Taken   44 41999999107793 milliseconds      Sum  4999950000      Time Taken   49 845000030472875 milliseconds       While loop  let arr       Array 100000  keys    function addUsingWhileLoop ar   let sum   0  let index   0  while  index  lt  ar length      sum    ar index     index        console log  Sum    sum      return sum    let t1   performance now    addUsingWhileLoop arr   let t2   performance now    console log  Time Taken      t2 - t1   milliseconds        Sum  4999950000      Time Taken   44 2499999771826 milliseconds      Sum  4999950000      Time Taken   44 01999997207895 milliseconds      Sum  4999950000      Time Taken   41 71000001952052 milliseconds       do-while  let arr       Array 100000  keys    function addUsingDoWhileLoop ar   let sum   0  let index   0  do      sum    index     index      while  index  lt  ar length      console log  Sum    sum        return sum    let t1   performance now    addUsingDoWhileLoop arr   let t2   performance now    console log  Time Taken      t2 - t1   milliseconds        Sum  4999950000      Time Taken   43 79500000504777 milliseconds      Sum  4999950000      Time Taken   43 47500001313165 milliseconds      Sum  4999950000      Time Taken   47 535000019706786 milliseconds       Reverse loop  let arr       Array 100000  keys    function addUsingReverseLoop ar      var sum 0     for  var i ar length  i--          sum  arr i           console log  Sum    sum        return sum    let t1   performance now    addUsingReverseLoop arr   let t2   performance now    console log  Time Taken      t2 - t1   milliseconds        Sum  4999950000      Time Taken   46 199999982491136 milliseconds      Sum  4999950000      Time Taken   44 96500000823289 milliseconds      Sum  4999950000      Time Taken   43 880000011995435 milliseconds       Reverse while loop  let arr       Array 100000  keys    function addUsingReverseWhileLoop ar       var sum   0      var i   ar length       while  i--            sum    ar i             console log  Sum    sum         return sum    var t1   performance now    addUsingReverseWhileLoop arr   var t2   performance now    console log  Time Taken      t2 - t1   milliseconds        Sum  4999950000      Time Taken   46 26999999163672 milliseconds      Sum  4999950000      Time Taken   42 97000000951812 milliseconds      Sum  4999950000      Time Taken   44 31500000646338 milliseconds       reduce  let arr       Array 100000  keys    let t1   performance now    sum   arr reduce  pv  cv    gt  pv   cv  0   console log  Sum    sum    let t2   performance now    console log  Time Taken      t2 - t1   milliseconds        Sum  4999950000      Time Taken   4 654999997001141 milliseconds      Sum  4999950000      Time Taken   5 040000018198043 milliseconds      Sum  4999950000      Time Taken   4 835000028833747 milliseconds       forEach  let arr       Array 100000  keys    function addUsingForEach ar     let sum   0    ar forEach item   gt        sum    item           console log  Sum    sum         return sum   let t1   performance now    addUsingForEach arr  let t2   performance now    console log  Time Taken      t2 - t1   milliseconds        Sum  4999950000      Time Taken   5 315000016707927 milliseconds      Sum  4999950000      Time Taken   5 869999993592501 mienter code herelliseconds      Sum  4999950000      Time Taken   5 405000003520399 milliseconds

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The fastest loop  according to this test is a while loop in reverse  var i   arr length  while  i--        So  this code might be the fastest you can get  Array prototype sum   function          var total   0      var i   this length        while  i--            total    this i              return total      Array prototype sum adds a sum method to the array class    you could easily make it a helper function instead

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Based on this test  for-vs-forEach-vs-reduce  and this  loops   I can say that   1  Fastest  for loop  var total   0   for  var i   0  n   array length  i  lt  n    i        total    array i       2  Aggregate  For you case you won t need this  but it adds a lot of flexibility   Array prototype Aggregate   function fn        var current           length   this length       if  length    0  throw  Reduce of empty array with no initial value        current   this 0        for  var i   1  i  lt  length    i                current   fn current  this i               return current       Usage   var total   array Aggregate function a b   return a   b       Inconclusive methods  Then comes forEach and reduce which have almost the same performance and varies from browser to browser  but they have the worst performance anyway

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While searching for the best method to sum an array  I wrote a performance test   In Chrome   reduce  seems to be vastly superior  I hope this helps     Performance test  sum of an array   var array    1  2  3  4  5  6  7  8  9  10     var result   0     Eval   console time  eval      for var i   0  i  lt  10000  i    eval  result        array join                console timeEnd  eval       Loop   console time  loop      for var i   0  i  lt  10000  i         result   0      for var j   0  j  lt  array length  j           result    parseInt array j                console timeEnd  loop       Reduce   console time  reduce      for var i   0  i  lt  10000  i    result   array reduce function pv  cv    return pv   parseInt cv      0     console timeEnd  reduce       While   console time  while      for var i   0  i  lt  10000  i         j   array length      result   0      while j--  result    array i         console timeEnd  while      eval  5233 000ms  loop  255 000ms  reduce  70 000ms  while  214 000ms

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Improvements    Your looping structure could be made faster        var count   0     for var i 0  n array length  i  lt  n  i                 count    array i           This retrieves array length once  rather than with each iteration   The optimization is made by caching the value     If you really want to speed it up          var count 0     for  var i array length  i--          count  array i          This is equivalent to a while reverse loop   It caches the value and is compared to 0  thus faster iteration   For a more complete comparison list  see my JSFiddle  Note  array reduce is horrible there  but in Firebug Console it is fastest     Compare Structures  I started a  JSPerf for array summations   It was quickly constructed and not guaranteed to be complete or accurate  but that s what edit is for

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one of the simplest  fastest  more reusable and flexible is   Array prototype sum   function          for var total   0 l this length l-- total  this l    return total        usage var array    1 2 3 4 5 6 7 8 9 10   array sum

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For your specific case  just use the reduce method of Arrays   var sumArray   function            Use one adding function rather than create a new one each        time sumArray is called     function add a  b            return a   b             return function arr            return arr reduce add                alert  sumArray  2  3  4

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Or you could do it the evil way   var a    1 2 3 4 5 6 7 8 9    sum   eval a join

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You should be able to use reduce   var sum   array reduce function pv  cv    return pv   cv     0     Source  And with arrow functions introduced in ES6  it s even simpler   sum   array reduce  pv  cv    gt  pv   cv  0

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What about summing both extremities  It would cut time in half  Like so   1  2  3  4  5  6  7  8  sum   0  2  3  4  5  6  7  sum   10  3  4  5  6  sum   19  4  5  sum   28  sum   37  One algorithm could be   function sum array arr       let sum   0          length   arr length          half   Math floor length 2       for  i   0  i  lt  half  i              sum    arr i    arr length - 1 - i            if  length 2           sum    arr half            return sum     It performs faster when I test it on the browser with performance now    I think this is a better way  What do you guys think

[javascript] Fastest JavaScript summation

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