I have a string, where I need to parse it as a float, but first I need to replace it, if it is not a number (an integer or a float), so I am trying to create an regular expression to do it

My tries results in NaN

One of my best tries is

var $replace = $text.replace(/^[^d.]*/, '');
var $float = parseFloat($replace);

Can anybody tell me, what I am doing wrong?

I have a string, where I need to parse it as a float, but first I need to replace it, if it is not a number (an integer or a float), so I am trying to create an regular expression to do it

My tries results in NaN

One of my best tries is

var $replace = $text.replace(/^[^d.]*/, '');
var $float = parseFloat($replace);

Can anybody tell me, what I am doing wrong?

• javascript
• regex

• your regex says to replace zero or more characters that are not a d or a . from the beginning of your string with nothing... What are you trying to replace/remove exactly? – J. Holmes Commented Nov 29, 2011 at 22:06
• I am trying to replace everything, that are not a digit (or a . (used in a float)) – The87Boy Commented Nov 29, 2011 at 22:13
• Why are you prepending a dollar sign to your variables? – NullUserException Commented Nov 29, 2011 at 22:26
• Can you give some examples of what $text might look like, and what you want $replace and $float to look like in those cases? – ruakh Commented Nov 30, 2011 at 15:12
• @NullUserException It depends on, which server-side programming language, I am using, and right here I am using PHP, which uses dollar signs in variables – The87Boy Commented Dec 4, 2011 at 20:05

3 Answers 3

If you really want to replace everything thats not a digit, then try this:

var $replace = $text.replace(/[^\d.]/g, '');
var $float = parseFloat($replace);

This will replace a string of "123a3d2" with a string of "12332".

It looks like you want to strip "non-numeric" characters from the beginning of the string before converting it to float. A naive approach would be:

var s = input.replace(/^[^\d.]+/, '');
var n = parseFloat(s);

This works for inputs like "foo123" but will fail on "foo.bar.123". To parse this we need a more sophisticated regexp:

var s = input.replace(/^(.(?!\d)|\D)+/, '');
var n = parseFloat(s);

Another method is to strip the input char by char until we find a valid float:

function findValidFloat(str) {
    for (var i = 0; i < str.length; i++) {
        var f = parseFloat(str.substr(i))
        if (!isNaN(f))
            return f;
    }
    return NaN;
}

if (! isNaN($text))
  $float = parseFloat($text);
else
  $float = 0; // or whatever