[javascript] Determine if string is in list in JavaScript

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 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.

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 < len; i++)
    {
        if (hay[i] == needle) { return true; }
    }

    return false;
}

var alist = ["test"];

console.log(in_list("test", alist));

Arrays have an indexOf method which can be used to search for strings:

js> a = ['foo', 'bar', 'baz']
foo,bar,baz
js> a.indexOf('bar')
1
js> a.indexOf('quux')
-1

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).

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!

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")) {
  // ...
}

A simplified version of SLaks' answer also works:

if ('abcdefghij'.indexOf(str) >= 0) {
    // Do something
}

....since strings are sort of arrays themselves. :)

If needed, implement the indexof function for Internet Explorer as described before me.

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
}

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<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.

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

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
}

Using indexOf(it doesn’t work with IE8).

if (['apple', 'cherry', 'orange', 'banana'].indexOf(value) >= 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)$/)) {

}

You can call indexOf:

if (['a', 'b', 'c'].indexOf(str) >= 0) {
    //do something
}

A trick I've used is

>>> ("something" in {"a string":"", "somthing":"", "another string":""})
false
>>> ("something" in {"a string":"", "something":"", "another string":""})
true

You could do something like

>>> a = ["a string", "something", "another string"];
>>> b = {};
>>> for(var i=0; i<a.length;i++){b[a[i]]="";} /* Transform the array in a dict */
>>> ("something" in b)
true