if/else defines plus or minus in function

Question

I have two practically identical functions. The only difference between them are one has + and one has -. These are used about 20 times in each function, so I'd love to make this simpler with a var.

I'm still very new to JavaScript, so I don't know where to start, but something like:

if ( blah blah ){
    var symbol = '-';
} else{
    var symbol = '+';
}

var example = value1 [symbol] value2;

Thanks

This is nothing to do with jQuery really, it's JavaScript. I've added the tag for you. — Rory McCrossan, Oct 31 '13 at 13:25
You can try these http://stackoverflow.com/questions/5834318/are-variable-operators-possible — Satpal, Oct 31 '13 at 13:29

score 23 · Accepted Answer · answered Oct 31 '13 at 13:26

23

Use this:

var modifier = (blah blah) ? 1 : -1;
var example = value1 + (modifier * value2);

answered Oct 31 '13 at 13:26

darthmaim

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how use it for * and /? – Kamil Dąbrowski Jul 02 '19 at 19:11
1

@KamilDąbrowski this only works for +/-. Check the [other answers](https://stackoverflow.com/a/19707843/2193252) for solutions that also work with different operators. – darthmaim Jul 08 '19 at 07:08
1

@KamilDąbrowski you can do a similar thing with * and / `4 * 4 / (isDivision ? (4 * 4) : 1)` – Moshe Sommers Dec 20 '19 at 16:24

score 6 · Answer 2 · answered Oct 31 '13 at 13:28

6

You could define an object containing functions, keyed by the operator. Something like this:

var operations = {
    '+': function(a, b) { return a + b; },
    '-': function(a, b) { return a - b; }
}

var x = operations[condition ? '+' : '-'](value1, value2);

I think @darthmaim has the nicest method though, but it depends if you need to use other operators, such as *, / or %.

answered Oct 31 '13 at 13:28

Rory McCrossan

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+1 - I was almost about to post the **same exact** thing. [Not kidding!] :-) – techfoobar Oct 31 '13 at 13:29

score 1 · Answer 3 · answered Oct 31 '13 at 13:25

1

why not so:

if ( blah blah ){
    var example = value1 - value2;
} else{
    var example = value1 + value2;
}

answered Oct 31 '13 at 13:25

Mikhail Timofeev

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score 1 · Answer 4 · answered Oct 31 '13 at 13:27

1

Well, you could use eval, but I would use a function like this:

var op;
if (condition) {
    op = function(a, b) { return a - b; };
} else {
    op = function(a, b) { return a + b; };
}

var example = op(value1, value2);

answered Oct 31 '13 at 13:27

FishBasketGordo

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score 0 · Answer 5 · answered Oct 31 '13 at 13:31

0

var math = {
    '+' : function(x,y) {return x + y;},
    '-' : function(x,y) {return x - y;}
}

var usePlus = true;
math[usePlus ? '+' : '-'](1,2) // returns 3

answered Oct 31 '13 at 13:31

aga

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if/else defines plus or minus in function

5 Answers5