Shorten JS if or statement

Question

Is there anyway to shorten something like this in Javascript: if (x == 1 || x == 2 || x == 3 || x == 4) to something like if (x == (1 || 2 || 3 || 4)) ?

If you're looking for syntax similar to what you posted, then no. You should consider that any roundabout way of shortening it will suffer a performance hit. — user113716, Feb 17 '11 at 17:51
Numbers were used as an example so using "if(x >0 && x < 5)" would not be useful if I am comparing strings. — John, Feb 17 '11 at 18:46

hugomg · Answer 1 · 2012-07-09T12:23:45.853

7

You can use use Array.indexOf

[1,2,3,4].indexOf(x) !== -1

You can also use objects as some kind of hash map:

//Note: Keys will be coerced to strings so
// don't use this method if you are looking for an object or if you need
// to distinguish the number 1 from the string "1"
my_values = {1:true, 2:true, 3:true, 'foo':true}
my_values.hasOwnProperty('foo')

By the way, in most cases you should usi the "===" strict equality operator instead of the == operator. Comparison using "==" may do lots of complicated type coercion and you can get surprising results sometimes.

edited Jul 09 '12 at 12:23

answered Feb 17 '11 at 17:38

hugomg

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Well *sometimes* "==" is useful, but you're probably right that "===" should be what a JavaScript programmer types automatically :-) – Pointy Feb 17 '11 at 17:49
1

speaking about coercion, object initializer does it thrice :-P – Free Consulting Feb 17 '11 at 18:06

score 2 · Answer 2 · answered Feb 17 '11 at 17:39

2

If your cases are not that simple to be expressed by this:

if (1 <= x && x <= 4)

You could use an array and indexOf:

if ([1,2,3,4].indexOf(x) > -1)

Note that indexOf might need to be re-implemented.

answered Feb 17 '11 at 17:39

Gumbo

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After removal of spaces, it's actually 1 character longer *(referring to `indexOf()`)*, but given a longer list of matches, it would be shorter. I guess it depends on actual code. – user113716 Feb 17 '11 at 17:44

score 1 · Answer 3 · answered Feb 17 '11 at 17:39

1

Not without writing a function that takes an array as an input and returns true/false, or some sort of array search. It would be hard to maintain/other devs to read. And it would be significantly slower. So just stick with the semantically correct longer version.

Also a good way to see if anything can be shortened significantly is to run it through the close compiler and see what it comes out with.

answered Feb 17 '11 at 17:39

Tom Gullen

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I second this. It's often a good idea to encapsulate complex checks like this into a func to communicate the meaning better. – Juho Vepsäläinen Feb 17 '11 at 17:47

score 1 · Answer 4 · answered Feb 17 '11 at 17:39

1

How about:

if (x > 0 && x < 5) {
}

answered Feb 17 '11 at 17:39

Kon

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I thought this, but then I realised John was presenting it as a simplified example not a case study so to speak. – Tom Gullen Feb 17 '11 at 17:40

score 0 · Answer 5 · answered Feb 17 '11 at 17:47

You could write a function:

function isAny(x) {
  for (var i = 1; i < arguments.length; ++i)
    if (arguments[i] === x) return true;
  return false;
}

Then you can say:

if (isAny(x, 1, 2, 3, 4)) { /* ... */ }

(Whether to use "===" or "==" would depend on the exact semantics you want.)

Shorten JS if or statement

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