In JavaScript how do I identify the first character in a string that doesn't match a regular expression?

Question

If I'm comparing a string with the correct spelling of "Honolulu" I'd like to know that the first mistake in "Hnolulo" is the missing first o, i.e. character 1.

Answer 1

It's not regex, but will work

var correct = "Honolulu";
var input   = "Hnolulu";

var v = validate(correct, input); // 1

function validate(correct, input) {
    var error = -1;
    var comp1 = correct.length > input.length ? correct : input;
    var comp2 = correct.length > input.length ? input : correct;

    for (var i=0; i<comp1.length; i++) {
        if (comp1.charAt(i) != comp2.charAt(i)) {
            error = i;
            break;
        }
    }
    return error;
}

FIDDLE