Determine if string is in list in JavaScript

Question

In SQL we can see if a string is in a list like so   Column IN   a    b    c     What s a good way to do this in JavaScript  It s so clunky to do this   if  expression1    expression2    str      a     str      b     str      c           do something     And I m not sure about the performance or clarity of this   if  expression1    expression2     a 1  b 1  c 1  str           do something     Or one could use the switch function   var str    a      flag   false   switch  str       case  a      case  b      case  c         flag   true     default     if  expression1    expression2    flag          do something     But that is a horrible mess  Any ideas   In this case  I have to use Internet nbsp Explorer 7 as it s for a corporate intranet page  So   a    b    c   indexOf str      -1 won t work natively without some syntax sugar

User · Answer

Most of the answers suggest the Array prototype indexOf method  the only problem is that it will not work on any IE version before IE9   As an alternative I leave you two more options that will work on all browsers   if   Foo Bar Baz  test str                  if  str match  Foo Bar Baz

User · Answer

A trick I ve used is   gt  gt  gt    something  in   a string       somthing       another string       false  gt  gt  gt    something  in   a string       something       another string       true   You could do something like   gt  gt  gt  a     a string    something    another string     gt  gt  gt  b        gt  gt  gt  for var i 0  i lt a length i    b a i           Transform the array in a dict     gt  gt  gt    something  in b  true

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A simplified version of SLaks  answer also works   if   abcdefghij  indexOf str   gt   0           Do something         since strings are sort of arrays themselves      If needed  implement the indexof function for Internet nbsp Explorer as described before me

User · Answer

Here s mine   String prototype inList function list       return  Array apply null  arguments  indexOf this toString       -1     var x    abc   if  x inList  aaa   bbb   abc        console log  yes    else     console log  no      This one is faster if you re OK with passing an array   String prototype inList function list       return  list indexOf this toString       -1     var x    abc   if  x inList   aaa   bbb   abc         console log  yes     Here s the jsperf  http   jsperf com bmcgin-inlsit

User · Answer

RegExp is universal  but I understand that you re working with arrays  So  check out this approach  I use to use it  and it s very effective and blazing fast   var str    some string with a   var list     a    b    c    var rx   new RegExp list join         rx test str     You can also apply some modifications  i e    One-liner  new RegExp list join       test str     Case insensitive  var rx   new RegExp list join      concat   i         And many others

User · Answer

Looks like you need to use in array function   jQuery -  inArray   Prototype -  Array indexOf  Or  see these examples if you are not using jQuery or Prototype    http   phpjs org functions in array 432 http   www bitrepository com equivalent-of-phps-in array-function html http   codingforums com showthread php t 63796   Stylistic note  variables named thisthing thatthing  should be named to tell you something about what they contain  noun

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Using indexOf it doesn   t work with IE8    if    apple    cherry    orange    banana   indexOf value   gt   0           found     To support IE8  you could implement Mozilla   s indexOf   if   Array prototype indexOf           indexOf polyfill code here     Regular Expressions via String prototype match  docs    if  fruit match    banana lemon mango pineapple

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Thanks for the question  and the solution using the Array indexOf method   I used the code from this solution to create a inList   function that would  IMO  make the writing simpler and the reading clearer   function inList psString  psList         var laList   psList split            var i   laList length      while  i--            if  laList i      psString  return true            return false      USAGE   if  inList  Houston    LA New York Houston          THEN do something when your string is in the list

User · Answer

In addition to indexOf  which other posters have suggested   using prototype s Enumerable include   can make this more neat and concise   var list     a    b    c    if  list include str          do stuff

User · Answer

You can call indexOf   if    a    b    c   indexOf str   gt   0          do something

User · Answer

My solution results in a syntax like this      Checking to see if var  column  is in array   a    b    c    if  column isAmong   a    b    c           Do something     And I implement this by extending the basic Object prototype  like this   Object prototype isAmong   function  MyArray      for  var a 0  a lt MyArray length  a            if  this     MyArray a                return true                  return false      We might alternatively name the method isInArray  but probably not inArray  or simply isIn   Advantages  Simple  straightforward  and self-documenting

User · Answer

Arrays have an indexOf method which can be used to search for strings   js gt  a     foo    bar    baz   foo bar baz js gt  a indexOf  bar   1 js gt  a indexOf  quux   -1

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I m surprised no one had mentioned a simple function that takes a string and a list   function in list needle  hay        var i  len       for  i   0  len   hay length  i  lt  len  i                  if  hay i     needle    return true               return false     var alist     test     console log in list  test   alist

User · Answer

EcmaScript 6 and up If you re using ES6 or higher  the cleanest way is to construct an array of the items and use Array includes    a    b    c   includes  b    This has some inherent benefits over indexOf because it can properly test for the presence of NaN in the list  and can match missing array elements such as the middle one in  1    2  to undefined  includes also works on JavaScript typed arrays such as Uint8Array  If you re concerned about browser support  such as for IE or Edge   you can check Array includes at CanIUse Com  and if you want to target a browser or browser version that s missing includes  I recommend polyfill io for polyfilling  Without An Array You could add a new isInList property to strings as follows  if   String prototype isInList      Object defineProperty String prototype   isInList         get       gt  function    args          let value   this valueOf          for  let i   0  l   args length  i  lt  l  i    1            if  arguments i      value  return true                return false                 Then use it like so   fox  isInList  weasel    fox    stoat      true  fox  isInList  weasel    stoat      false  You can do the same thing for Number prototype  Note that Object defineProperty cannot be used in IE8 and earlier  or very old versions of other browsers  However  it is a far superior solution to String prototype isInList   function           because using simple assignment like that will create an enumerable property on String prototype  which is more likely to break code  Array indexOf If you are using a modern browser  indexOf always works  However  for IE8 and earlier you ll need a polyfill  If indexOf returns -1  the item is not in the list  Be mindful though  that this method will not properly check for NaN  and while it can match an explicit undefined  it can   t match a missing element to undefined as in the array  1    2   Polyfill for indexOf or includes in IE  or any other browser version lacking support If you don t want to use a service like polyfill io as mentioned above  you can always include in your own source code standards-compliant custom polyfills  For example  Mozilla Developer Network has one for indexOf  In this situation where I had to make a solution for Internet Explorer 7  I  quot rolled my own quot  simpler version of the indexOf   function that is not standards-compliant  if   Array prototype indexOf       Array prototype indexOf   function item          var i   this length        while  i--             if  this i      item  return i                return -1          However  I don t think modifying Array prototype is the best answer in the long term  Modifying Object and Array prototypes in JavaScript can lead to serious bugs  You need to decide whether doing so is safe in your own environment  Of primary note is that iterating an array  when Array prototype has added properties  with for     in will return the new function name as one of the keys  Array prototype blah   function     console log  blah       let arr    1  2  3   for  let x in arr    console log x        Result  0 1 2 blah    Extra member iterated over   Your code may work now  but the moment someone in the future adds a third-party JavaScript library or plugin that isn t zealously guarding against inherited keys  everything can break  The old way to avoid that breakage is  during enumeration  to check each value to see if the object actually has it as a non-inherited property with if  arr hasOwnProperty x   and only then work with that x  The new ES6 ways to avoid this extra-key problem are   Use of instead of in  for  let x of arr   However  unless you can guarantee that all of your code and third-party libraries strictly stick to this method  then for the purposes of this question you ll probably just want to use includes as stated above   Define your new properties on the prototype using Object defineProperty    as this will make the property  by default  non-enumerable  This only truly solves the problem if all the JavaScript libraries or modules you use also do this

[javascript] Determine if string is in list in JavaScript

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