Set custom HTML5 required field validation message

Code snippet

Since this answer got very much attention, here is a nice configurable snippet I came up with:

/**
  * @author ComFreek <https://stackoverflow.com/users/603003/comfreek>
  * @link https://stackoverflow.com/a/16069817/603003
  * @license MIT 2013-2015 ComFreek
  * @license[dual licensed] CC BY-SA 3.0 2013-2015 ComFreek
  * You MUST retain this license header!
  */
(function (exports) {
    function valOrFunction(val, ctx, args) {
        if (typeof val == "function") {
            return val.apply(ctx, args);
        } else {
            return val;
        }
    }

    function InvalidInputHelper(input, options) {
        input.setCustomValidity(valOrFunction(options.defaultText, window, [input]));

        function changeOrInput() {
            if (input.value == "") {
                input.setCustomValidity(valOrFunction(options.emptyText, window, [input]));
            } else {
                input.setCustomValidity("");
            }
        }

        function invalid() {
            if (input.value == "") {
                input.setCustomValidity(valOrFunction(options.emptyText, window, [input]));
            } else {
               input.setCustomValidity(valOrFunction(options.invalidText, window, [input]));
            }
        }

        input.addEventListener("change", changeOrInput);
        input.addEventListener("input", changeOrInput);
        input.addEventListener("invalid", invalid);
    }
    exports.InvalidInputHelper = InvalidInputHelper;
})(window);

Usage

→ jsFiddle

<input id="email" type="email" required="required" />

InvalidInputHelper(document.getElementById("email"), {
  defaultText: "Please enter an email address!",

  emptyText: "Please enter an email address!",

  invalidText: function (input) {
    return 'The email address "' + input.value + '" is invalid!';
  }
});

More details

• defaultText is displayed initially
• emptyText is displayed when the input is empty (was cleared)
• invalidText is displayed when the input is marked as invalid by the browser (for example when it’s not a valid email address)

You can either assign a string or a function to each of the three properties.
If you assign a function, it can accept a reference to the input element (DOM node) and it must return a string which is then displayed as the error message.

Compatibility

Tested in:

• Chrome Canary 47.0.2
• IE 11
• Microsoft Edge (using the up-to-date version as of 28/08/2015)
• Firefox 40.0.3
• Opera 31.0

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Old answer

You can see the old revision here: https://stackoverflow.com/revisions/16069817/6