Why does assignment with help from ternary operator doesn't work as expected in JS?

Question

var a = 0;
var param = 'add';
while(a < 50){
    console.log(a); //prints out values from 0 to 49
    if(param === 'add'){
        a = a + 1;
    }else{
        a = a - 1;
    }
}

While being very simple and doing its job, I would like to make this code shorter

while(a < 50){
    console.log(a);
    a = a + (param === 'add')? 1 : -1;
}

But a never grows and stays 1. Could anyone explain such behavior?

All the operations before `?` are considered as the condition part of the ternary. — Teemu, Jan 12 '22 at 10:15
Shorter is not the same as better. Your original code is much easier to read. And works. — Andy, Jan 12 '22 at 10:17
I agree with Andy, although I would change `a = a + 1` to `a++` and `a = a - 1` to `a--`. — Ivar, Jan 12 '22 at 10:18
Possible duplicate: [Operator precedence with Javascript Ternary operator](https://stackoverflow.com/questions/1788917/operator-precedence-with-javascript-ternary-operator) — Andreas, Jan 12 '22 at 10:19
Also if param is not add, your loop will never stop - `prints out values from 0 to 49 OR from 0 to -infinity` — mplungjan, Jan 12 '22 at 10:22

www.admiraalit.nl · Answer 1 · 2022-01-12T10:21:09.917

1

The expression is evaluated as

a = (a + (param === 'add')) ? 1 : -1;

which boils down to

a = 1;

You may solve this by writing

a = a + ((param === 'add') ? 1 : -1);

or even shorter:

a += (param === 'add') ? 1 : -1;

edited Jan 12 '22 at 10:21

answered Jan 12 '22 at 10:16

www.admiraalit.nl

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Why not just `a += param === 'add' ? 1 : -1;` ..? – Teemu Jan 12 '22 at 10:17
Sure, I have appended this to my answer. – www.admiraalit.nl Jan 12 '22 at 10:22

Why does assignment with help from ternary operator doesn't work as expected in JS?

1 Answers1