From http://www.w3schools.com (Copyright Refsnes Data)

WMLScript replace() Function

The replace() function replaces a part of a string with a new string, and returns the result.

n = String.replace(string, oldvalue, newvalue)

Part	Description
n	The string returned from the function
string	The original string
oldvalue	The value that is going to be replaced
newvalue	The value that will replace oldvalue

var a = String.replace("world","wor","bo");
var b = String.replace("world", "ld","ry");

a = "bold"
b = "worry"