Check variable equality against a list of values

Question

I m checking a variable  say foo  for equality to a number of values  For example   if  foo    1    foo    3    foo    12                    The point is that it is rather much code for such a trivial task  I came up with the following   if  foo in  1  1  3  1  12  1                     but also this does not completely appeal to me  because I have to give redundant values to the items in the object   Does anyone know a decent way of doing an equality check against multiple values

User · Answer

You can write if foo in L 10 20 30   if you define L to be  var L   function         var obj           for var i 0  i lt arguments length  i            obj arguments i     null       return obj

User · Answer

You could use an array and indexOf   if   1 3 12  indexOf foo   gt  -1

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In ECMA2016 you can use the includes method  It s the cleanest way I ve seen   Supported by all major browsers  if  1 3 12  includes foo

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Using the answers provided  I ended up with the following   Object prototype in   function         for var i 0  i lt arguments length  i           if arguments i     this  return true      return false      It can be called like   if foo in 1  3  12                      Edit  I came across this  trick  lately which is useful if the values are strings and do not contain special characters  For special characters is becomes ugly due to escaping and is also more error-prone due to that    foo bar something  test str     To be more precise  this will check the exact string  but then again is more complicated for a simple equality test      foo bar something    test str

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Now you may have a better solution to resolve this scenario  but other way which i preferred   const arr    1 3 12  if  arr includes foo        it will return true if you  foo  is one of array values else false      code here         I preferred above solution over the indexOf check where you need to check index as well   includes docs  if   arr indexOf  foo       -1

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Also  since the values against which you re checking the result are all unique you can use the Set prototype has   as well     x000D   x000D  var valid    1  3  12   x000D  var goodFoo   3  x000D  var badFoo   55  x000D   x000D     Test x000D  console log  new Set valid  has goodFoo     x000D  console log  new Set valid  has badFoo     x000D   x000D   x000D

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This is easily extendable and readable   switch  foo        case 1      case 3      case 12                         break      case 4      case 5      case 6             something else         break     But not necessarily easier

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I simply used jQuery inArray function and an array of values to accomplish this   myArr     A    B    C    C-     var test     inArray  C   myArr       returns index of 2 returns -1 if not in array  if test  gt   0     true

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var a    1 2 3    if   a indexOf  1       -1         Note that indexOf is not in the core ECMAScript  You ll need to have a snippet for IE and possibly other browsers that dont support Array prototype indexOf   if   Array prototype indexOf      Array prototype indexOf   function searchElement     fromIndex              use strict        if  this     void 0    this     null        throw new TypeError         var t   Object this       var len   t length  gt  gt  gt  0      if  len     0        return -1       var n   0      if  arguments length  gt  0              n   Number arguments 1          if  n     n          n   0        else if  n     0  amp  amp  n      1   0   amp  amp  n     - 1   0           n    n  gt  0    -1    Math floor Math abs n               if  n  gt   len        return -1       var k   n  gt   0             n             Math max len - Math abs n   0        for    k  lt  len  k                if  k in t  amp  amp  t k      searchElement          return k            return -1

User · Answer

If you have access to Underscore  you can use the following   if    contains  1  3  12   foo                  contains used to work in Lodash as well  prior to V4   now you have to use includes  if    includes  1  3  12   foo       handleYellowFruit

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This is a little helper arrow function  const letters     A    B    C    D     function checkInList arr  val      return arr some arrVal   gt  val     arrVal      checkInList letters   E         false checkInList letters   A         true  More info here

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I liked the accepted answer  but thought it would be neat to enable it to take arrays as well  so I expanded it to this   Object prototype isin   function         for var i   arguments length  i--             var a   arguments i           if a constructor     Array                for var j   a length  j--                   if a j     this  return true                    else if a    this  return true            return false     var lucky   7      more    7  11  42   lucky isin 2  3  5  8  more    true   You can remove type coercion by changing    to

User · Answer

For posterity you might want to use regular expressions as an alternative  Pretty good browser support as well  ref  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects String match Browser compatibility   Try this  if  foo toString   match    1 3 12            document write  Regex me IN lt br gt       else       document write  Regex me OUT lt br gt

[javascript] Check variable equality against a list of values

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