convert string to a number in javascript

Question

I want to parse a user input which contains longitude and latitude. What I want to do is to coerce a string to a number, preserving its sign and decimal places. But what I want to do is to display a message when user's input is invalid. Which one should I follow

parseFloat(x)

second

new Number(x)

third

~~x

fourth

+x

Answer 1

I'd use Number(x), if I had to choose between those two, because it won't allow trailing garbage. (Well, it "allows" it, but the result is a NaN.)

That is, Number("123.45balloon") is NaN, but parseFloat("123.45balloon") is 123.45 (as a number).

As Mr. Kling points out, which of those is "better" is up to you.

edit — ah, you've added back +x and ~~x. As I wrote in a comment, +x is equivalent to using the Number() constructor, but I think it's a little risky because of the syntactic flexibility of the + operator. That is, it'd be easy for a cut-and-paste to introduce an error. The ~~x form is good if you know you want an integer (a 32-bit integer) anyway. For lat/long that's probably not what you want however.

Answer 2

The first one is better. It is explicit, and it is correct. You said you want to parse floating point numbers. ~~x will give you an integer.