Solo `+` in JavaScript

Question

I came across some weird JavaScript code:

var a, b; // integers set somewhere;

var c = +b;

someFunc(+a);

What does that + mean here? In my tests I cannot see any effect from it in JavaScript, but at the same time it is valid JavaScript.

What is it really, and why would anyone ever use it?

[see documentation on unary +](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Unary_plus_()) — Kevin L, Jul 19 '16 at 17:32

Jordan · Accepted Answer · 2016-07-19T17:35:23.913

3

It is a unary operator. It converts the value to a Number, if it can.

+'4' === 4

+'4.23' === 4.23

+'true' === 1

edited Jul 19 '16 at 17:35

answered Jul 19 '16 at 17:32

Jordan

Not just integers. – elclanrs Jul 19 '16 at 17:34
You're right, too broad. Edited to number. – Jordan Jul 19 '16 at 17:35
Wow, after years of writing in JavaScript this one escaped me somehow, I always used `* 1` instead :) Thank you! – vitaly-t Jul 19 '16 at 17:40
It is worth noting that if for some reason the value is undefined let's say `+a`, here `a` is `undefined` it'll return `NaN`. For more check [this](https://stackoverflow.com/a/64175820/5375291) – Debu Shinobi Jul 07 '22 at 10:42

score 2 · Answer 2 · answered Jul 19 '16 at 17:32

2

It converts the value to a Number

answered Jul 19 '16 at 17:32

William B

2 Answers2