JSFiddle - React, Tailwind, and code Playground

by Graham Fairweather

HTML

<input id="test" type="text" />

JavaScript

/*jslint maxerr: 50, indent: 4, browser: true */

(function () {
    "use strict";

    function addEvent(elem, event, fn) {
        if (typeof elem === "string") {
            elem = document.getElementById(elem);
        }

        function listenHandler(e) {
            var ret = fn.apply(null, arguments);

            if (ret === false) {
                e.stopPropagation();
                e.preventDefault();
            }

            return ret;
        }

        function attachHandler() {
            window.event.target = window.event.srcElement;

            var ret = fn.call(elem, window.event);

            if (ret === false) {
                window.event.returnValue = false;
                window.event.cancelBubble = true;
            }

            return ret;
        }

        if (elem.addEventListener) {
            elem.addEventListener(event, listenHandler, false);
        } else {
            elem.attachEvent("on" + event, attachHandler);
        }
    }

    function verify(e) {
        var target = e.target, // shouldn't be needed: || e.srcElement;
            value = target.value,
            char = String.fromCharCode(e.keyCode || e.charCode);

        if (value.charAt(0) === "-") {
            if (char === "+") {
                e.target.value = value.slice(1);
            }
        } else if (char === "-") {
            e.target.value = char + value;
            return false;
        }

        value += char;
        return parseFloat(value) === +value;
    }

    addEvent("test", "keypress", verify);
}());