replace.js

var myString = 'EXAMPLEstring';
var myNewString = myString.replace(/[A-Z]/g, '0');
console.log(myNewString);

function replaceFunc (a, b, c) {
  console.log(a, b, c);
  return a.toLowerCase();
}

var myOtherString = myString.replace(/[A-Z]/g, replaceFunc);

console.log(myOtherString);

// This function expects three arguments. There could be more depending on how many "capture" groups are included in the regular expression.
// The first argument (a) is always the full text of the match.
// Since there are no capture groups, the second argument (b) is the zero-based index of the match within the string.
// The final argument (c) is the full text of the string being searched.
// As shown in this example, because the match is global (using the "g" identifier in the RegEx), the three arguments are logged for each match.