In SQL Server, I could say:
WHERE X IN(1,2) How would you rewrite the following in JavaScript:
if (X==1 || X==2) {} asked Mar 9, 2011 at 21:53
- I wonder if I could write an IN function.– Phillip SennCommentedMar 9, 2011 at 21:54
- 4Your question doesn't make sense. You have written valid JavaScript.– OdedCommentedMar 9, 2011 at 21:55
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9 Answers
Use indexOf to see if x is in an array.
if([1,2].indexOf(x) !== -1) 
answered Mar 9, 2011 at 21:56
- Browser compatibility of Array.indexOf looks good, starts with MSIE 9 for example developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…– Open SEOCommentedApr 21, 2020 at 16:16
Using Array .includes method.
if ([1, 2].includes(x)) { // array has x } 
- This is a better answer for modern browsers, but I'm afraid IE doesn't support it. Ref: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…– Ryan WCommentedJan 5, 2017 at 16:19
- 6It's good practice on Stack Overflow to add an explanation as to why your solution should work. For more information read How To Answer.CommentedJan 5, 2017 at 17:16
- Yes, IE won't work. Use it with polyfill or in conjunction with a transpiler (e.g. Babel / Typescript)– vitkonCommentedJan 5, 2017 at 22:39
Try using an array, and then its .indexOf().
var myNumbers = [1,2]; var foo = 4; var bar = 1; var exists = (myNumbers.indexOf(bar) > -1); //true var notExists = (myNumbers.indexOf(foo) > -1); //false answered Mar 9, 2011 at 21:56
- 3IE7 and below don't support it apparently.. here's more info and a drop in fallback soledadpenades.com/2007/05/17/arrayindexof-in-internet-explorer– adamJLevCommentedMar 9, 2011 at 22:14
There's no silver bullet. There will be a few gotchas.
If you do indexOf as some answers suggest, you need to remember that Array.indexOf is not supported in all browsers, so you need to provide your own fallback. Also this will have a performance of O(n) since it needs to traverse the whole array, which might not be ideal if you're dealing with a huge array.
If you use the in operator as other answers suggest, you need to remember that in Javascript object's properties are always strings, so don't expect === checks to work if you're checking for numbers.
In this particular example you suggested, I would just go for the good old if (X==1 || X==2).
- simple and super clean answer that assure to run on all browsers.CommentedJan 13, 2019 at 20:26
if (x in {1:true, 2:true}) { } Or, if you want to abstract it you could do it like this http://snook.ca/archives/javascript/testing_for_a_v
function oc(a) { var o = {}; for(var i=0;i
Still... not the most scalable thing to be doing
- 2This fails If
xcontains an identifier of an “inherited” property:var x = "constructor"; x in {1:true, 2:true}yields true.– GumboCommentedMar 9, 2011 at 21:58 - Thats interesting, to be honest it isn't really the nicest construct anyway.CommentedMar 9, 2011 at 22:03
Requires Javascript 1.6
if ((new Array(1, 2)).indexOf(X) != -1) { } 
I know we have in_array() function in PHP, but I never heard of a similar function in JS. I think you gotta do it the old way:
function contains(a, obj) { var i = a.length; while (i--) { if (a[i] === obj) { return true; } } return false; } Function to convert the array into an object literal
function oc(a) { var o = {}; for(var i=0;i<a.length;i++) { o[a[i]]=''; } return o; } You can call the function like
if( name in oc(['Tom', 'Harry','Sue']) ) { ... } answered Mar 9, 2011 at 21:58
Just fun:
if (X*X+1*2 == (1+2)*X) {} or self-explaining:
if ((X-1)*(X-2) == 0) {} answered Mar 9, 2011 at 22:19
