Check if an element is present in an array

Question

The function I am using now to check this is the following   function inArray needle haystack        var count haystack length      for var i 0 i lt count i                  if haystack i    needle  return true             return false      It works  What I m looking for is whether there is a better way of doing this

User · Answer

You can use the  contains function from the underscore js library to achieve this   if    contains haystack  needle       console log  Needle found

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I benchmarked it multiple times on Google Chrome 52  but feel free to copypaste it into any other browser s console       1500 ms  includes    2700 ms when I used the polyfill   var array    0 1 2 3 4 5 6 7 8 9    var result   0   var start   new Date   getTime    for var i   0  i  lt  10000000  i        if array includes  test       true   result        console log new Date   getTime   - start         1050 ms  indexOf  var array    0 1 2 3 4 5 6 7 8 9    var result   0   var start   new Date   getTime    for var i   0  i  lt  10000000  i        if array indexOf  test    gt  -1   result        console log new Date   getTime   - start         650 ms  custom function  function inArray target  array        Caching array length doesn t increase the performance of the for loop on V8  and probably on most of other major engines        for var i   0  i  lt  array length  i             if array i      target              return true               return false      var array    0 1 2 3 4 5 6 7 8 9    var result   0   var start   new Date   getTime    for var i   0  i  lt  10000000  i        if inArray  test   array      true   result        console log new Date   getTime   - start

User · Answer

Just use indexOf   haystack indexOf needle   gt   0   If you want to support old Internet Explorers   lt  IE9   you ll have to include your current code as a workaround though   Unless your list is sorted  you need to compare every value to the needle  Therefore  both your solution and indexOf will have to execute n 2 comparisons on average  However  since indexOf is a built-in method  it may use additional optimizations and will be slightly faster in practice  Note that unless your application searches in lists extremely often  say a 1000 times per second  or the lists are huge  say 100k entries   the speed difference will not matter

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ECMAScript 2016 incorporates an includes   method for arrays that specifically solves the problem  and so is now the preferred method   1  2  3  includes 2          true  1  2  3  includes 4          false  1  2  3  includes 1  2       false  second parameter is the index position in this array at which to begin searching   As of JULY 2018  this has been implemented in almost all major browsers  if you need to support an older browser a polyfill is available  Edit  Note that this returns false if the item in the array is an object  This is because similar objects are two different objects in JavaScript

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Code   function isInArray value  array      return array indexOf value   gt  -1      Execution   isInArray 1   1 2 3       true   Update  2017    In modern browsers which follow the ECMAScript 2016  ES7  standard  you can use the function Array prototype includes  which makes it way more easier to check if an item is present in an array    x000D   x000D  const array    1  2  3   x000D  const value   1  x000D  const isInArray   array includes value   x000D  console log isInArray      true x000D   x000D   x000D

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Single line code   will return true or false     arr indexOf  val   1

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Since ECMAScript6  one can use Set    var myArray     A    B    C    var mySet   new Set myArray   var hasB   mySet has  B       true var hasZ   mySet has  Z       false

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In lodash you can use   includes  which also aliases to   contains   You can search the whole array     includes  1  2  3   1      true   You can search the array from a starting index     includes  1  2  3   1  1       false  begins search at index 1    Search a string     includes  pebbles    eb        true  string contains eb    Also works for checking simple arrays of objects     includes    user    fred    age   40     fred          true   includes    user    fred    age   false    false       true   One thing to note about the last case is it works for primitives like strings  numbers and booleans but cannot search through arrays or objects    includes    user    fred    age                   false   includes    user    1 2 3    age         3        false

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You can use indexOf But not working well in the last version of internet explorer  Code   function isInArray value  array      return array indexOf value   gt  -1      Execution   isInArray 1   1 2 3       true   I suggest you use the following code   function inArray needle  haystack     var length   haystack length   for  var i   0  i  lt  length  i       if  haystack i     needle    return true      return false

[javascript] Check if an element is present in an array

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