javascriptregexstringnumbers

How can I extract a number from a string in JavaScript?

I have a string in JavaScript (e.g., #box2), and I just want the 2 from it.

I tried:

var thestring = $(this).attr('href');
var thenum = thestring.replace(/(^.+)(\w\d+\w)(.+$)/i, '$2');
alert(thenum);

It still returns #box2 in the alert. How can I get it to work?

It needs to accommodate for any length number attached on the end.

Solution

  • For this specific example,

     var thenum = thestring.replace(/^\D+/g, ''); // Replace all leading non-digits with nothing

    In the general case:

     thenum = "foo3bar5".match(/\d+/)[0] // "3"

    Here's a bonus: regex generator.

    function getre(str, num) {
  if(str === num)
    return 'nice try';
  var res = [/^\D+/g,/\D+$/g,/^\D+|\D+$/g,/\D+/g,/\D.*/g, /.*\D/g,/^\D+|\D.*$/g,/.*\D(?=\d)|\D+$/g];
  for(var i = 0; i < res.length; i++)
    if(str.replace(res[i], '') === num)
      return 'num = str.replace(/' + res[i].source + '/g, "")';
  return 'no idea';
};

function update() {
  $ = function(x) { return document.getElementById(x) };
  var re = getre($('str').value, $('num').value);
  $('re').innerHTML = 'Numex speaks: <code>' + re + '</code>';
}
    <p>Hi, I'm Numex, the Number Extractor Oracle.
<p>What is your string? <input id="str" value="42abc"></p>
<p>What number do you want to extract? <input id="num" value="42"></p>
<p><button onclick="update()">Insert Coin</button></p>
<p id="re"></p>