JavaScript: Simple way to check if variable is equal to one of two or more values?

Is there an easier way to determine if a variable is equal to a range of values, such as:

if x === 5 || 6 

rather than something obtuse like:

if x === 5 || x === 6

?

You can stash your values inside an array and check whether the variable exists in the array by using [].indexOf:

if([5, 6].indexOf(x) > -1) {
  // ...
}

If -1 is returned then the variable doesn't exist in the array.

Depends on what sort of test you're performing. If you've got static strings, this is very easy to check via regular expressions:

if (/^[56ab]$/.test(item)) {
//-or-
if (/^(foo|bar|baz|fizz|buzz)$/.test(item)) {
    doStuff();
} else {
    doOtherStuff();
}

If you've got a small set of values (string or number), you can use a switch:

switch (item) {
case 1:
case 2:
case 3:
    doStuff();
    break;
default:
    doOtherStuff();
    break;
}

If you've got a long list of values, you should probably use an array with ~arr.indexOf(item), or arr.contains(item):

vals = [1,3,18,3902,...];
if (~vals.indexOf(item)) {
    doStuff();
} else {
    doOtherStuff();
}

_{Unfortunately Array.prototype.indexOf isn't supported in some browsers. Fortunately a polyfill is available. If you're going through the trouble of polyfilling Array.prototype.indexOf, you might as well add Array.prototype.contains.}

Depending on how you're associating data, you could store a dynamic list of strings within an object as a map to other relevant information:

var map = {
    foo: bar,
    fizz: buzz
}
if (item in map) {
//-or-
if (map.hasOwnProperty(item)) {
    doStuff(map[item]);
} else {
    doOtherStuff();
}

_{in will check the entire prototype chain while Object.prototype.hasOwnProperty will only check the object, so be aware that they are different.}

It's perfectly fine. If you have a longer list of values, perhaps you can use the following instead:

if ([5,6,7,8].indexOf(x) > -1) {
}

Yes. You can use your own function. This example uses .some:

var foo = [ 5, 6 ].some(function(val) {
     return val === x;
   });

foo; // true

This is what I've decided to use:

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;
}

You would use it like this:

var fav   = 'pear',
    fruit = ['apple', 'banana', 'orange', 'pear'],
    plu   = [4152, 4231, 3030, 4409];

if (fav.isin(fruit, plu, 'eggs', 'cheese')) {
	//do something cool
}

The advantages are:

• it works in IE < 9;
• it reads naturally from left to right;
• you can feed it arrays or separate values.

If you don't want to allow type coercion (indexOf does not), change the two == to ===. As it stands:

fav = "4231";
plu.indexOf(fav) //-1
fav.isin(plu)    //true

no, there might be a few tricks that are case specific but in general i write code like this:

if (someVariable === 1 ||
    someVariable === 2 ||
    someVariable === 7 ||
    someVariable === 12 ||
    someVariable === 14 ||
    someVariable === 19) {

    doStuff();
    moreStuff();

} else {
    differentStuff();
}

The simple answer is no. You can use a switch statement, which is easier to read if you are comparing a lot of string values, but using it for two values wouldn't look any better.

[Edit] this seems to work, but as Dan pointed out, it is actually a false positive. Do not use this method. I leave it here for educational purposes.

Easiest way I know :

a = [1,2,3,4,5];

if(3 in a) alert("true"); // will alert true

Tested in Chrome console. Not sure if it works in other browsers.