The Book of JavaScript, 2nd Edition

parseInt() [FF, IE 3]

Converts a string to an integer as long as the first character is a number. If the first character is not a number, parseInt() returns NaN (not a number). If the string is a number followed by letters, parseInt() grabs the first set of digits in the string.

Example:

var the_string = "123abc456";
var the_numbers = parseInt(the_string);

The variable the_numbers contains 123.