Get the first integers in a string with JavaScript

If the number is at the start of the string:

("123 hello everybody 4").replace(/(^\d+)(.+$)/i,'$1'); //=> '123'

If it's somewhere in the string:

(" hello 123 everybody 4").replace( /(^.+)(\w\d+\w)(.+$)/i,'$2'); //=> '123'

And for a number between characters:

("hello123everybody 4").replace( /(^.+\D)(\d+)(\D.+$)/i,'$2'); //=> '123'

[addendum]

A regular expression to match all numbers in a string:

"4567 stuff is fun4you 67".match(/^\d+|\d+\b|\d+(?=\w)/g); //=> ["4567", "4", "67"]

You can map the resulting array to an array of Numbers:

"4567 stuff is fun4you 67"
  .match(/^\d+|\d+\b|\d+(?=\w)/g)
  .map(function (v) {return +v;}); //=> [4567, 4, 67]

Including floats:

"4567 stuff is fun4you 2.12 67"
  .match(/\d+\.\d+|\d+\b|\d+(?=\w)/g)
  .map(function (v) {return +v;}); //=> [4567, 4, 2.12, 67]

If the possibility exists that the string doesn't contain any number, use:

( "stuff is fun"
   .match(/\d+\.\d+|\d+\b|\d+(?=\w)/g) || [] )
   .map(function (v) {return +v;}); //=> []

So, to retrieve the start or end numbers of the string 4567 stuff is fun4you 2.12 67"

// start number
var startingNumber = ( "4567 stuff is fun4you 2.12 67"
  .match(/\d+\.\d+|\d+\b|\d+(?=\w)/g) || [] )
  .map(function (v) {return +v;}).shift(); //=> 4567

// end number
var endingNumber = ( "4567 stuff is fun4you 2.12 67"
  .match(/\d+\.\d+|\d+\b|\d+(?=\w)/g) || [] )
  .map(function (v) {return +v;}).pop(); //=> 67

var str = "some text and 856 numbers 2";
var match = str.match(/\d+/);
document.writeln(parseInt(match[0], 10));

If the strings starts with number (maybe preceded by whitespace), simple parseInt(str, 10) is enough. parseInt will skip leading whitespace.

10 is necessary, because otherwise string like 08 will be converted to 0 (parseInt in most implementations consider numbers starting with 0 as octal).