var addEvent = (function () { if (document.addEventListener) { return function (element, type, handler) { element.addEventListener(type, handler, false); }; } else if (document.attachEvent) { return function (element, type, handler) { element.attachEvent('on' + type, function () { handler.apply(element, arguments); }); }; } else { return function (element, type, handler) { element['on' + type] = function () { return handler.apply(element, arguments); }; }; }})(),getClassElements = function (parentElement, classname) { var all, element, classArr = [], classElements = []; if (parentElement.getElementsByClassName) { return parentElement.getElementsByClassName(classname); } else { all = parentElement.getElementsByTagName('*'); for (var i = 0, len = all.length; i < len; i++) { element = all[i]; classArr = element && element.className && element.className.split(' '); if (classArr) { for (var j = 0; j < classArr.length; j++) {  if (classArr[j] === classname) {  classElements.push(element);  } } } } return classElements; }},delegate = function () { // 參數：element, type, [selector,] handler var args = arguments, element = args[0], type = args[1], handler; if (args.length === 3) { handler = args[2]; return addEvent(element, type, handler); } if (args.length === 4) { selector = args[2]; handler = args[3]; return addEvent(element, type, function (event) { var event = event || window.event, target = event.target || event.srcElement, quickExpr = /^(?:[a-zA-Z]*#([/w-]+)|(/w+)|[a-zA-Z]*/.([/w-]+))$/, match, idElement, elements, tagName, count = 0, len; if (typeof selector === 'string') { match = quickExpr.exec(selector); if (match) {  // #ID selector  if (match[1]) {  idElement = document.getElementById(match[1]);  tagName = match[0].slice(0, match[0].indexOf('#'));  // tag selector  } else if (match[2]) {  elements = element.getElementsByTagName(selector);  // .class selector  } else if (match[3]) {  elements = getClassElements(element, match[3]);  tagName = match[0].slice(0, match[0].indexOf('.'));  } } if (idElement) {  if ( tagName ? tagName === idElement.nodeName.toLowerCase() && target === idElement : target === idElement ) {  return handler.apply(idElement, arguments);  } } else if (elements) {  for (len = elements.length; count < len; count++) {  if ( tagName ? tagName === elements[count].nodeName.toLowerCase() && target === elements[count] : target === elements[count] ) {  return handler.apply(elements[count], arguments);  }  } } } }); }};

handler.apply(idElement, arguments);handler.apply(elements[count], arguments);

<style>#outer {padding: 50px; background-color: lightpink;}#inner {padding: 30px; background-color: aliceblue;}#paragraph1, #paragraph3 {background-color: cadetblue}</style>

<div id="outer">outer <div id="inner">inner <p id="paragraph1" class="parag1">paragraph1</p> <p id="paragraph2" class="parag">paragraph2</p> <span>span</span> <p id="paragraph3" class="parag">paragraph3</p> </div></div>

var outer = document.getElementById('outer');delegate(outer, 'click', function () { console.log(this.id); // outer});

delegate(outer, 'click', 'p', function () { console.log(this.id); //點擊 paragraph1 元素，輸出其id為 "paragraph1"});

(function () { var $ = function (element) { return new _$(element); }; var _$ = function (element) { this.element = element && element.nodeType === 1 ? element : document; }; _$.prototype = { constructor: _$, addEvent: function (type, handler, useCapture) { var element = this.element; if (document.addEventListener) { element.addEventListener(type, handler, (useCapture ? useCapture : false)); } else if (document.attachEvent) { element.attachEvent('on' + type, function () {  handler.apply(element, arguments); }); } else { element['on' + type] = function () {  return handler.apply(element, arguments); }; } return this; }, getClassElements: function (classname) { var element = this.element, all, ele, classArr = [], classElements = []; if (element.getElementsByClassName) { return element.getElementsByClassName(classname); } else { all = element.getElementsByTagName('*'); for (var i = 0, len = all.length; i < len; i++) {  ele = all[i];  classArr = ele && ele.className && ele.className.split(' ');  if (classArr) {  for (var j = 0; j < classArr.length; j++) {  if (classArr[j] === classname) {  classElements.push(ele);  }  }  } } return classElements; } }, delegate: function () { //參數：type, [selector,] handler var self = this, element = this.element, type = arguments[0], handler; if (arguments.length === 2) { handler = arguments[1]; return self.addEvent(type, handler); } else if (arguments.length === 3) { selector = arguments[1]; handler = arguments[2]; return self.addEvent(type, function (event) {  var event = event || window.event,  target = event.target || event.srcElement,  quickExpr = /^(?:[a-zA-Z]*#([/w-]+)|(/w+)|[a-zA-Z]*/.([/w-]+))$/,  match,  idElement,  elements,  tagName,  count = 0,  len;  if (typeof selector === 'string') {  match = quickExpr.exec(selector);  if (match) {  // #ID selector  if (match[1]) {  idElement = document.getElementById(match[1]);  tagName = match[0].slice(0, match[0].indexOf('#'));  // tag selector  } else if (match[2]) {  elements = element.getElementsByTagName(selector);  // .class selector  } else if (match[3]) {  elements = self.getClassElements(match[3]);  tagName = match[0].slice(0, match[0].indexOf('.'));  }  }  if (idElement) {  if ( tagName ? tagName === idElement.nodeName.toLowerCase() && target === idElement ? target === idElement ) {  return handler.apply(idElement, arguments);  }  } else if (elements) {  for (len = elements.length; count < len; count++) {  if ( tagName ? tagName === elements[count].nodeName.toLowerCase() && target === elements[count] : target === elements[count] ) {   return handler.apply(elements[count], arguments);  }  }  }  } }); } } }; window.$ = $; return $;}());

var outer = document.getElementById('outer');$(outer).delegate('click', '.parag', function (event) { console.log(this.id);});