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

I think it's very fun to come up with ways to solve this. Below are some.
(All functions below assume argument is a single character. Change to n[0] to enforce it)

Method 1:

function isCharDigit(n){
  return !!n.trim() && n > -1;
}

Method 2:

function isCharDigit(n){
  return !!n.trim() && n*0==0;
}

Method 3:

function isCharDigit(n){
  return !!n.trim() && !!Number(n+.1); // "+.1' to make it work with "." and "0" Chars
}

Method 4:

var isCharDigit = (function(){
  var a = [1,1,1,1,1,1,1,1,1,1];
  return function(n){
    return !!a[n] // check if `a` Array has anything in index 'n'. Cast result to boolean
  }
})();

Method 5:

function isCharDigit(n){
  return !!n.trim() && !isNaN(+n);
}

Test string:

var str = ' 90ABcd#?:.+', char;
for( char of str ) 
  console.log( char, isCharDigit(char) );