Ternary operator and assignment: better way for not calling the same function twice

Question

I have this code line:

const my_v = !isNaN(parseInt(jQuery('#id').val())) ? parseInt(jQuery('#id').val()) : 0;

As you can see I call the parseInt function twice.
I was wondering if there is a way to do that assignment calling the function once.

You right. Since I do not know the new javascript specs I was asking if there is a way to do with 1 code line. — Giacomo M, Sep 17 '19 at 13:02
Also, you could just use `const my_v = parseInt(jQuery('#id').val()) || 0` - no need for a conditional operator in this case. — VLAZ, Sep 17 '19 at 13:02
Note that you also call the `jQuery('#id')` and `val()` functions twice. — Heretic Monkey, Sep 17 '19 at 13:02
You *could* do it in the same line but it's not worth the hassle - makes it harder to read. — VLAZ, Sep 17 '19 at 13:02

score 5 · Accepted Answer · answered Sep 17 '19 at 13:02

5

The result of parseInt() is going to be either a number or NaN, so you can use ||:

const my_v = parseInt(jQuery("#id").val()) || 0;

Now, in general I would caution anyone against using parseInt(), because (by design) it accepts strings like "123hello world" as valid numbers (123 in this case). You can use the Number() constructor or plain unary + to coerce a string to a number. If you don't want a fractional part, you can use Math.floor() or Math.round(), and you can check numerically to see if there's a fractional part if that should be considered an error.

answered Sep 17 '19 at 13:02

Pointy

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Yes I realize that `NaN` is also a number; you know what I mean :) – Pointy Sep 17 '19 at 13:05
In this case parseInt is exactly what I need. Strip characters and keep numbers. – Giacomo M Sep 17 '19 at 13:14
@GiacomoM OK, it's just my standard warning because it can surprise people – Pointy Sep 17 '19 at 13:31

score 1 · Answer 2 · answered Sep 17 '19 at 13:02

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Sure using an IIFE:

 (n => !isNaN(n) ? n : 0)(parseInt(jQuery('#id').val()))

But seriously, usea local variable.

answered Sep 17 '19 at 13:02

Jonas Wilms

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score 1 · Answer 3 · answered Sep 17 '19 at 13:08

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With one const you can declare more than one variable.

const idValue = parseInt(jQuery('#id').val()), my_v = isNaN(idValue) ? 0 : idValue;

answered Sep 17 '19 at 13:08

mbojko

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Nina Scholz · Answer 4 · 2019-09-17T13:04:40.743

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If you have already a stringed integer value, you could just take a number or zero as default value.

const my_v = +jQuery('#id').val() || 0;

If not, get first the value and then the integer part.

const my_v = Math.floor(+jQuery('#id').val() || 0);

edited Sep 17 '19 at 13:04

answered Sep 17 '19 at 13:02

Nina Scholz

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Could yield a different result for a value like `10.a` or even `10.5` – VLAZ Sep 17 '19 at 13:03
@Rajesh, the value is already a number, then no need to parse it again. – Nina Scholz Sep 17 '19 at 13:07

Ternary operator and assignment: better way for not calling the same function twice

4 Answers4