Javascript shorthand OR operation

Question

I have feeling this must be a duplicate, but I've been unable to find anything, probably due to different wording, or just because there really is nothing better.

I am generating kind of huge chunk of JS code, which "ORs" object properties with variables, while identifiers don't necessarily match. It looks like this (values are boolean):

a.borderline = a.borderline || borderline;
a.st1 = a.st1 || st;
a.ref64 = a.ref64 || ref;
a.unfortunatelySometimesQuiteLongIndentifier123 = a.unfortunatelySometimesQuiteLongIndentifier123 || unfortunatelySometimesQuiteLongIndentifier;
...

To make it leaner I tried something like

a.st1 |= st;

but it makes a.st1 integer instead of boolean and I don't want to add another line with double negation to retype it back to boolean.

Using intuition I also tried ||=, which did not help :)

Is there any better (shorter) way of writing these commands?

Note: I cannot process the commands using a loop, because the commands are not executed all at once, instead they are spread in small chunks in the rest of the code (which was omitted for simplicity).

In Javascript, no, not that I know of. You may want to look into coffeescript, which has a `?=`. — James Duffy, Apr 30 '14 at 16:57
Is there a specific reason why `1` and `0` are objectionable? — Patrick Q, Apr 30 '14 at 16:59
@PatrickQ Later I am making JSON out of it and sending it somewhere. To comply with the protocol I have to distinguish between `0` and `false`. Yet I cannot convert all zeroes to `false`, as there are also valid numeric values. — Erlik, Apr 30 '14 at 17:39

score 3 · Accepted Answer · edited May 23 '17 at 11:50

3

No, there is no shorthand OR operator in javascript. Coffeescript however does provide ||= and ?= to support this idiom.

Is there any better (shorter) way of writing these commands?

In your case, you're amending the a object instead of assigning to variables. You might do this in a loop fashion:

function amendWith(target, source)
    for (var p in source)
        if (!target[p])
            target[p] = source[p];
    return target;
}

amendWith(a, {
    borderline: borderline,
    st1: st,
    ref64: ref,
    unfortunatelySometimesQuiteLongIndentifier123: unfortunatelySometimesQuiteLongIndentifier
    …
});

edited May 23 '17 at 11:50

Community

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answered Apr 30 '14 at 16:58

Bergi

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Unfortunately, I can't use the loop (added the **Note** after you had probably read the question), but I'll definitely investigate Coffeescript option. Thanks! – Erlik Apr 30 '14 at 17:42
Yeah, I didn't notice the edit. You might however post your full code (either in a new question at [cr.SE], in some paste service online, or into your question) so that we can see whether there is a better pattern then. – Bergi Apr 30 '14 at 17:55
OK, cool! Coffeescript will work for me. Luckily, it can be compiled into the "long" code after passing the bottleneck, so CS saves the day. Btw interestingly, the `a.st1 ||= st` is compiled into `a.st1 || (a.st1 = st);`, which took me a while to understand, but well.. it works :) – Erlik Apr 30 '14 at 18:15

Mike · Answer 2 · 2014-04-30T18:08:12.603

1

I'm not sure this is any shorter, but just as an alternative idea you could put the OR logic in a function and then loop through your values.

function myFunctionName(value1, value2) {
  return value1 || value2;
}

//names are property names of object 'a' that you want to set, values are the alternate (default) values
var myMapping = {borderline:borderline, st1:st, reallyLongName123:reallyLongName}; 

for (temp in myMapping) {
  a.temp = myFunctionName(a[temp], myMapping[temp]);
}

Since your unable to use a loop and you don't know all the values ahead of time, you could try adding the function to your object 'a'

a.test = function(propName, otherValue) {
  this[propName] = this[propName] || otherValue;
};

a.test("borderline", borderline);

edited Apr 30 '14 at 18:08

answered Apr 30 '14 at 17:10

Mike

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Not shorter since you're *still* repeating `a.borderline` twice. – Mike Christensen Apr 30 '14 at 17:19
Exactly, the main problem is repeating of the `a.borderline` part, which can sometimes be very long. – Erlik Apr 30 '14 at 17:40
@Erlik I updated the code to use a loop, does that make it any cleaner? – Mike Apr 30 '14 at 17:43
@monkybonk05 Yes, now it's not repeated. However, I cannot use loop, neither the static initialization `var myMapping = {...`. I am obtaining the values in a scattered way as well as using them (see the **Note** later added to my question). – Erlik Apr 30 '14 at 17:46
1

@Erlik Are you able to add functions to object 'a'? If so, check out my update. – Mike Apr 30 '14 at 18:08
@monkybonk05 That's actually very interesting and yet so simple. `a` is not the only object changed this way, but I can modify it to `test = function(a, propName, otherValue) {...` Thanks! +1 – Erlik Apr 30 '14 at 18:21

Javascript shorthand OR operation

2 Answers2