I’m asking this just for the sake of shaving a few bytes.
I know I can use +x (unary plus) instead of Number(x). Is there a difference between those and parseFloat?
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Answer
The difference between parseFloat and Number
parseFloat/parseInt is for parsing a string, while Number/+ is for coercing a value to a number. They behave differently. But first let’s look at where they behave the same:
parseFloat('3'); // => 3
Number('3'); // => 3
parseFloat('1.501'); // => 1.501
Number('1.501'); // => 1.501
parseFloat('1e10'); // => 10000000000
Number('1e10'); // => 10000000000
So as long as you have standard numeric input, there’s no difference. However, if your input starts with a number and then contains other characters, parseFloat truncates the number out of the string, while Number gives NaN (not a number):
parseFloat('1x'); // => 1
Number('1x'); // => NaN
In addition, Number understands hexadecimal input while parseFloat does not:
parseFloat('0x10'); // => 0
Number('0x10'); // => 16
But Number acts weird with empty strings or strings containing only white space:
parseFloat(''); // => NaN
Number(''); // => 0
parseFloat(' rnt'); // => NaN
Number(' rnt'); // => 0
On the whole, I find Number to be more reasonable, so I almost always use Number personally (and you’ll find that a lot of the internal JavaScript functions use Number as well). If someone types '1x' I prefer to show an error rather than treat it as if they had typed '1'. The only time I really make an exception is when I am converting a style to a number, in which case parseFloat is helpful because styles come in a form like '3px', in which case I want to drop the 'px' part and just get the 3, so I find parseFloat helpful here. But really which one you choose is up to you and which forms of input you want to accept.
Note that using the unary + operator is exactly the same as using Number as a function:
Number('0x10'); // => 16
+'0x10'; // => 16
Number('10x'); // => NaN
+'10x'; // => NaN
Number('40'); // => 40
+'40'; // => 40
So I usually just use + for short. As long as you know what it does, I find it easy to read.