Check if character is number?

Question

I need to check whether justPrices[i].substr(commapos+2,1).

The string is something like: \"blabla,120\"

In this case it would check whether \'0

Answer 1

You can use this:

function isDigit(n) {
    return Boolean([true, true, true, true, true, true, true, true, true, true][n]);
}

Here, I compared it to the accepted method: http://jsperf.com/isdigittest/5 . I didn't expect much, so I was pretty suprised, when I found out that accepted method was much slower.

Interesting thing is, that while accepted method is faster correct input (eg. '5') and slower for incorrect (eg. 'a'), my method is exact opposite (fast for incorrect and slower for correct).

Still, in worst case, my method is 2 times faster than accepted solution for correct input and over 5 times faster for incorrect input.