using javascript operator-- new to me

Question

It's all pretty clear except for one line-- in the code two vars are set to -1. Then they are used like this:

var cur = -1, prv = -1;
prv = +cur; // what does this do?
console.log(prv); // results -1
console.log(cur); // results -1

I'm familiar with the += usage-- but I haven't seen this usage before and don't understand why what appears to be (-1) + (-1) = -1

What am I missing?

Pointy · Accepted Answer · 2013-10-03 19:02:07Z

4

It's the unary plus operator and it converts its operand to a number.

In the code you posted, it'd have no net effect. If, however, it had been this:

var cur = "-1", prv = -1;
prv = +cur;

then "prv" would be set to the numeric value -1 instead of the string that's referenced by "cur".

answered Oct 3, 2013 at 19:02

Pointy

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2 Comments

@Pointy-- thanks! To be clear, is this essentially a shorthand way to type cast? Like using parseInt?

@user101289 yes exactly - just a quick way of doing it. If the value can't be converted, of course, you get a NaN.