Javascript replace undefined error ends but not replace continues [duplicate]

Answer 1

try this (not sure about cross-browser):

newaltr = bodytext.replace(avidno, altrstr, "g");

Answer 2

Your regex includes ^ and $, which force the regex to match only the whole string. That's probably the reason why replace fails.

Try this (untested):

var avidno = '(800)123 1234';
var bodytext = document.body.innerHTML;
var newaltr;

function validate () {
    var format = '\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})';
    var bodytext, altrstr, newtext;

    if (RegExp('^' + format + '$').test(avidno)) {
        // This could be done in a single line, but this way it's clearer
        bodytext = document.body.innerHTML;
        altrstr = '<span>'+avidno+'</span>';
        newtext = bodytext.replace(RegExp(format, 'g'), altrstr);
        document.body.innerHTML = newtext;

        // Valid international phone number
    } else {
        alert('uupss');
        // Invalid international phone number
    }
}
validate();