javascript权威指南第22章高级技巧
HTML
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div style="position: fixed;background:red;width:300px;height: 200px;">
<button id="my-btn">确定</button>
<div id='myDiv' style="background: blue;width:50px;height:50px">
</div>
</div>
<div class="draggable" style="position: fixed;background:red;width:300px;height: 200px;">
<div id='status' style="width: 100px;height:100px;"></div>
</div>
<script type="text/javascript" src="Expression.js"></script>
</body>
</html>
JS
//22.1
//22.1.1 安全的类型检测
var value = new Array();
var isArray = value instanceof Array;
var isArray = typeof value; //比如正则表达式操作符会返回function
//由于所有类型都是派生于Object 对象
function isArray(value) {
return Object.prototype.toString.call(value) == '[object Array]';
}
function isFunction(value) {
return Object.prototype.toString.call(value) == '[object Function]';
}
function isRegExp(value) {
return Object.prototype.toString.call(value) == '[object RegExp]';
}
// 21.1.2 作用域安全的构造函数
function Person(name, age, job) {
this.name = name;
this.age = age;
this.job = job;
}
//正确构造
var person = new Person('Nicholas', 29, 'Software Engineer'); //构造一个对象
//意外的构造
person = Person('Nicholas', 29, 'Software Engineer'); //这样被当函数执行，this指向window
//安全的构造对象
function Polygon(sides) {
if (this instanceof Polygon) {
this.sides = sides;
this.getArea = function () {
return 0;
}
} else {
return new Polygon(sides);
}
}
//窃取模式继承存在的问题
function Rectangle(width, height) {
Polygon.call(this, 2);
this.width = width;
this.height = height;
this.getArea = function () {
return this.width * this.height;
};
}
var rect = new Rectangle(5, 10);
alert(rect.sides); //undefined 因为基类 Polygon 是作用域安全的
// 当new Rectangle() 构造函数已经锁定this =Rectangle
// 通过 Polygon.call(this,2);构造函数时候 this!=Polygon
// 此时 Rectangle this 与 Polygon this 不同域因此不会被继承属性
//利用原型继承方式可以解决这个问题
Rectangle.prototype = new Polygon(0);
//22.1.3 懒性载入函数
//假如页面js脚本会重复多次执行
//因为浏览器是在当下一旦确定就不会变
//因此这里只要第一次判断出支持的请求方式后
//就直接覆盖新的声明函数给当前函数。
//从而实现简化逻辑if语句
function CreateXMLHttpRequest() {
if (typeof XMLHttpRequest != undefined) {
return function () {
return new XMLHttpRequest();
}
} else if (typeof ActiveXObject != undefined) {
return function () {
return new ActiveXObject('');
}
}
}
//22.1.4 函数绑定
var handler = {
message: 'Event handled',
handleClick: function (event) {
alert(this.message);
}
};
var btn = document.getElementById('my-btn');
btn.addEventListener('click', function (event) {
handler.handleClick(event);
}, false);
//创建一个闭包(闭包是隔断作用域)
function bind(fn, context) {
return function () {
return fn.apply(context, arguments);
}
}
btn.addEventListener('click', bind(handler.handleClick, handler), false);
//22.1.5 函数柯里化
//柯里化通用方式
function curry(fn, context) {
var args = Array.prototype.slice.call(arguments, 2); //取从数组下表2开始后的参数（外部参数）
//前2参数是fn context
return function () {
var innerArgs = Array.prototype.slice.call(arguments); //闭包函数参数，即当前闭包函数
var finalArgs = args.concat(innerArgs); //外部函数参数和闭包函数链接起来
return fn.apply(context, finalArgs);
};
}
//22.2 防篡改对象
// 22.2.1 不可拓展对象
Object.preventExtensions(person); //设置该对象不可拓展
if (Object.isExtensible(person)) {
}
//22.2.2 密封的对象
Object.seal(person);
if (Object.isSealed(person)) {
}
//22.2.3 冻结的对象
Object.freeze(person);
//22.3.1 重复的定时器
var interval = 250;
setTimeout(function () {
//处理逻辑
var div = document.getElementById('myDiv');
var left = parseInt(div.style.left) + 5;
div.style.left = left + "px";
if (left < 200) {
setTimeout(arguments.callee, interval);
}
}, interval);
//22.3.2 Yielding Processes
function chunk(array, process, context) {
setTimeout(function () {
var item = array.shift();
process.call(context, item);
if (array.length > 0) {
setTimeout(arguments.callee, 100);
}
}, 100);
}
var data = [12, 123, 1234, 453, 436];
function printValue(item) {
var div = document.getElementById('myDiv');
div.innerHTML += item + "<br>";
}
chunk(data, printValue);
//22.3.3 函数节流
var processor = {
timeoutId: null,
//实际进行处理的方法
performProcessing: function () {
//实际执行的代码
},
process: function () {
clearTimeout(this.timeoutId); //清除当前定时器，执行代码逻辑后再设置定时器
var that = this; //引用this指针
this.timeoutId = setTimeout(function () {
that.performProcessing();
}, 100);
}
};
//尝试开始执行
processor.process();
//简化模式
function throttle(method, context) {
clearTimeout(method.tId);
method.tId = setTimeout(function () {
method.call(context);
}, 100);
};
//22.4 自定义事件
function EventTarget() {
this.handlers = {};
}
EventTarget.prototype = {
constructor: EventTarget,
addHandler: function (type, handler) {
if (typeof this.handlers[type] == 'undefined') {
this.handlers[type] = [];
}
this.handlers[type].push(handler);
},
fire: function (event) {
if (!event.target) {
event.target = this;
}
if (this.handlers[event.type] instanceof Array) {
var handlers = this.handlers[event.type];
for (var i = 0, len = handlers.length; i < len; i++) {
handlers[i](event);
}
}
},
removeHandler: function (type, handler) {
if (this.handlers[type] instanceof Array) {
var handlers = this.handlers[type];
for (var i = 0, len = handlers.length; i < len; i++) {
if (handlers[i] == handler) {
break;
}
}
handlers.splice(i, 1);
}
}
}
//事件使用
function handleMessage(event) {
alert('Message received' + event.message);
}
//创建一个新对象
var target = new EventTarget();
//添加事件处理程序
target.addHandler('message', handleMessage);
//触发事件
target.fire({ type: 'message', message: 'Hello world!' });
//删除事件
target.removeHandler('message', handleMessage);
//再次触发，应该没有处理程序
target.fire({ type: 'message', message: 'Hello world!' });
//22.5 拖放
// var DragDrop = function () {
// var dragging = null;
// var diffx = 0;
// var diffY = 0;
// function handleEvent(event) {
// //获取事件和目标
// event = event ? event : window.event;
// var target = event.target || event.srcElement;
// //确定事件类型
// switch (event.type) {
// case "mousedown":
// if (target.className.indexOf("draggable") > -1) {
// dragging = target;
// diffx = event.clientX - target.offsetLeft;
// diffY = event.clientY - target.offsetTop;
// target.style.cursor = 'move';
// }
// break;
// case "mousemove":
// if (dragging !== null) {
// dragging.style.left = (event.clientX - diffx) + "px";
// dragging.style.top = (event.clientY - diffY) + "px";
// }
// break;
// case "mouseup":
// dragging = null;
// target.style.cursor = 'default';
// break;
// }
// };
// //公共接口
// return {
// enable: function () {
// document.addEventListener('mousedown', function (event) {
// handleEvent(event);
// }, false);
// document.addEventListener('mousemove', function (event) {
// handleEvent(event);
// }, false);
// document.addEventListener('mouseup', function (event) {
// handleEvent(event);
// }, false);
// },
// disable: function () {
// document.removeEventListener('mousedown', function (event) {
// handleEvent(event);
// }, false);
// document.removeEventListener('mousemove', function (event) {
// handleEvent(event);
// }, false);
// document.removeEventListener('mouseup', function (event) {
// handleEvent(event);
// }, false);
// }
// }
// }();
//DragDrop.enable();
//添加自定义事件
var _DragDrop = function () {
var dragdrop = new EventTarget(),
dragging = null,
diffX, diffY;
function handleEvent(event) {
//获取事件和目标
event = event ? event : window.event;
var target = event.target || event.srcElement;
//确定事件类型
switch (event.type) {
case "mousedown":
if (target.className.indexOf("draggable") > -1) {
dragging = target;
diffx = event.clientX - target.offsetLeft;
diffY = event.clientY - target.offsetTop;
target.style.cursor = 'move';
dragdrop.fire({ type: 'dragstart', target: dragging, x: event.clientX, y: event.clientY });
}
break;
case "mousemove":
if (dragging !== null) {
dragging.style.left = (event.clientX - diffx) + "px";
dragging.style.top = (event.clientY - diffY) + "px";
//触发自定义事件
dragdrop.fire({ type: 'drag', target: dragging, x: event.clientX, y: event.clientY });
}
break;
case "mouseup":
dragdrop.fire({ type: 'dragend', target: dragging, x: event.clientX, y: event.clientY });
dragging = null;
target.style.cursor = 'default';
break;
}
};
//公共接口
dragdrop.enable =function(){
document.addEventListener('mousedown', function (event) {
handleEvent(event);
}, false);
document.addEventListener('mousemove', function (event) {
handleEvent(event);
}, false);
document.addEventListener('mouseup', function (event) {
handleEvent(event);
}, false);
};
dragdrop.disable =function(){
document.removeEventListener('mousedown', function (event) {
handleEvent(event);
}, false);
document.removeEventListener('mousemove', function (event) {
handleEvent(event);
}, false);
document.removeEventListener('mouseup', function (event) {
handleEvent(event);
}, false);
}
return dragdrop;
}(); //表示实例化当前对象
_DragDrop.addHandler('dragstart',function(event){
var status =document.getElementById('status');
status.innerHTML ="Started dragging"+event.target.id;
});
_DragDrop.addHandler('drag',function(event){
var status =document.getElementById('status');
status.innerHTML +="<br/>Dragged "+event.target.id+"to（"+event.x+","+event.y+")";
});
_DragDrop.addHandler('dragend',function(event){
var status =document.getElementById('status');
status.innerHTML +="<br/>Dropped "+event.target.id+"at"+event.x+","+event.y+")";
});
_DragDrop.enable();
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