1.使用FileReader实现前端图片预览
<input type="file"><br><img src="" height="200" alt="Image preview area..." title="preview-img">
var fileInput = document.querySelector('input[type=file]');
var previewImg = document.querySelector('img');
fileInput.addEventListener('change', function () {
var file = this.files[0];
var reader = new FileReader();
reader.addEventListener('load', function () {
previewImg.src = reader.result;
}, false);
reader.readAsDataURL(file);
}, false);
2.取到页面中所有的checkbox怎么做？(不使用第三方框架)
var doc = document,
domList = doc.getElementsByTagName('input'),
checkBoxList = [],
len = domList.length;
while (len--) {
if (domList[len].type === 'checkbox') {
checkBoxList.push(domList[len]);
}
}
3.JavaScript模版引擎小实例
<div class="result"></div>
<script type="template" id="template">
<h2>
<a href="{{href}}">
{{title}}
</a>
</h2>
<img src="{{imgSrc}}" width="300" height="100" alt="{{title}}"/>
</script>
数据:
var data = [
{
title: "",
href: "",
imgSrc: ""
},
...
];
方法一：
var doc = document,
template = doc.querySelector('#template').innerHTML,
result = doc.querySelector('.result'),
fragment = '';
for (var i = 0, len = data.length; i < len; i++) {
fragment += template
.replace(/\{\{title\}\}/, data[i].title)
.replace(/\{\{href\}\}/, data[i].href)
.replace(/\{\{imgSrc\}\}/, data[i].imgSrc)
}
result.innerHTML = fragment;
方法二：
var doc = document,
template = doc.querySelector('#template').innerHTML,
result = doc.querySelector('.result'),
attachTemplateToData;
attachTemplateToData = function (template, data) {
var i = 0,
len = data.length,
fragment = '';
function replace(obj) {
var t, key, reg;
for (key in obj) {
reg = new RegExp('{{' + key + '}}', 'ig');
t = (t || template).replace(reg, obj[key]);
}
return t;
}
for (; i < len; i++) {
fragment += replace(data[i]);
}
return fragment;
};
result.innerHTML = attachTemplateToData(template, data);
4.实现JS函数重载
var people = {
values: ["Dean Edwards", "Sam Stephenson", "Alex Russell", "Dean Tom"]
};
function addMethod(object, name, fn) {
var old = object[name];
object[name] = function () {
if (fn.length === arguments.length) {
return fn.apply(this, arguments);
} else if (typeof old === 'function') {
return old.apply(this, arguments);
}
}
}
addMethod(people, "find", function () {
return this.values;
});
addMethod(people, "find", function (firstName) {
var ret = [];
for (var i = 0; i < this.values.length; i++) {
if (this.values[i].indexOf(firstName) === 0) {
ret.push(this.values[i]);
}
}
return ret;
});
addMethod(people, "find", function (firstName, lastName) {
var ret = [];
for (var i = 0; i < this.values.length; i++) {
if (this.values[i] === (firstName + ' ' + lastName)) {
ret.push(this.values[i]);
}
}
return ret;
});
console.log(people.find());
console.log(people.find("Sam"));
console.log(people.find("Dean Edwards"));
5.JS跨浏览器绑定事件函数
常规实现方法:
//跨浏览器添加事件
function addHandler(target, eventType, handler) {
//检测浏览器类型，并且重写addHandler方法
if (target.addEventListener) {
addHandler = function (target, eventType, handler) {
target.addEventListener(eventType, handler, false);
}
} else { //IE
addHandler = function (target, eventType, handler) {
target.attachEvent("on" + eventType, handler);
}
}
//调用新的函数
addHandler(target, eventType, handler);
}
//跨浏览器移除事件
function removeHandler(target, eventType, handler) {
//检测浏览器类型，并且重写addHandler方法
if (target.addEventListener) {
removeHandler = function (target, eventType, handler) {
target.removeEventListener(eventType, handler, false);
}
} else { //IE
removeHandler = function (target, eventType, handler) {
target.detachEvent("on", eventType, handler);
}
}
target.detachEvent("on" + eventType, handler);
}
优化方法:
//绑定事件
var addHandler = document.body.addEventListener ?
function (target, eventType, handler) {//DOM2
target.addEventListener(eventType, handler, false);
} :
function (target, eventType, handler) {//IE
target.attachEvent("on" + eventType, handler);
};
//移除事件
var removeHandler = document.body.removeEventListener ?
function (target, eventType, handler) {
target.removeEventListener(eventType, handler, false);
} :
function (target, eventType, handler) {
target.detachEvent("on" + eventType, handler);
};
6.JS单体模式
var shoppingCar = (function () {
//这个是由购物车构造器所创建的实例
var instance;
//购物车的构造器函数
function Trolley() {
this.date = new Date().getDate();//实例属性，当前日期
}
//原型属性，一个返回当前日期的方法
Trolley.prototype.getDate = function () {
return this.date;
};
//暴露出去的公共API
return function () {
//如果实例不存在，那么就调用Trolley构造器实例化一个
if (!instance) {
instance = new Trolley();
}
//将实例返回外部
return instance;
}
}());
var a = new shoppingCar();
var b = new shoppingCar();
console.log(a === b);//true
7.使用prototype属性定义的对象方法
var dom = function () {};
dom.Show = function () {
alert("Show Message");
};
dom.prototype.Display = function () {
alert("Property Message");
};
dom.Display(); //error
dom.Show(); //Show Message
var d = new dom();
d.Display(); //Property Message
d.Show(); //error
1、不使用prototype属性定义的对象方法，是静态方法，只能直接用类名进行调用！另外，此静态方法中无法使用this变量来调用对象其他的属性！
2、使用prototype属性定义的对象方法，是非静态方法，只有在实例化后才能使用！其方法内部可以this来引用对象自身中的其他属性！
8.闭包实现结果缓存
var CachedSearchBox = (function () {
var cache = {},
table = [];
return {
attachSearchBox: function (dsid) {
if (dsid in cache) { //如果结果在缓存中
return cache[dsid]; //直接返回缓存中的对象
}
var fsb = new uikit.webctrl.SearchBox(dsid);//新建
cache[dsid] = fsb;//更新缓存
if (count.length > 100) {
delete cache[shift()];
}
return fsb;
},
clearSearchBox: function (dsid) {
if (dsid in cache) {
cache[dsid].clearSelection();
}
}
}
})();
CachedSearchBox.attachSearchBox('input');
我们开发中会碰到很多情况，设想我们有一个处理过程很耗时的函数对象，每次调用都会花费很长时间，
那么我们就需要将计算出来的值存储起来，当调用这个函数的时候，首先在缓存中查找，如果找不到，则进行计算，然后更新缓存并返回值，如果找到了，直接返回查找到的值即可。闭包正是可以做到这一点，因为它不会释放外部的引用，从而函数内部的值可以得以保留。
9.闭包实现封装
var person = function () {
var name = "Default";
return {
getName: function () {
return name;
},
setName: function (newName) {
name = newName;
}
}
}();
console.log(person.name);//undefined
console.log(person.getName());//Default
person.setName("GoodMan");
console.log(person.getName());//GoodMan
10.闭包实现类和继承
function Person() {
var name = "default";
return {
getName: function () {
return name;
},
setName: function (newName) {
name = newName;
}
}
}
var p = new Person();
p.setName('Tom');
console.log(p.getName());
var Jack = function () {
};
Jack.prototype = new Person();//继承自Person
Jack.prototype.Say = function () { //添加私有方法
console.log("Hello,my name is Jack");
};
var j = new Jack();
j.setName("Jack");//Tom
j.Say();//Hello,my name is Jack
console.log(j.getName());//Jack
11.如何判断某变量是否为数组数据类型
if (typeof Array.isArray === "undefined") {
Array.isArray = function (arg) {
return Object.prototype.toString.call(arg) === "[object Array]"
};
}
12.Javascript继承-借用构造函数
var Widget = function (name) {
this.messages = [];
};
Widget.prototype.type = 'Widget';
var SubWidget = function (name) {
Widget.apply(this, Array.prototype.slice.call(arguments));
this.name = name;
};
SubWidget.prototype = Widget.prototype;
var sub1 = new SubWidget('foo');
var sub2 = new SubWidget('bar');
sub1.messages.push('foo');
sub2.messages.push('bar');
console.log(sub1.messages);//foo
console.log(sub2.messages);//bar
13.Javascript原型-封装
var Dialog = (function () {
function Dialog() {
}
Dialog.prototype = {
init: function () {
console.log("ok");
}
};
return Dialog;
}());
var d = new Dialog();
d.init();//ok
14.通过闭包修正函数的上下文（浏览器不支持解决方案）
if (!('bind' in Function.prototype)) {
Function.prototype.bind = function () {
var fn = this,
context = arguments[0],
args = Array.prototype.slice.call(arguments, 1);
return function () {
return fn.apply(context, args.concat(arguments));
}
}
}
15.优化JavaScript的构造函数(new关键字的使用)
方法一：
function User(name, age) {
if (typeof Object.create === 'undefined') {
Object.create = function (prototype) {
function C() {
C.prototype = prototype;
return new C();
}
}
}
var self = this instanceof User ? this : Object.create(User.prototype);
self.name = name;
self.age = age;
return self;
}
方法二：
function Programmer(name, company, expertise) {
if (!(this instanceof Programmer)) {
return new Programmer(name, company, expertise);
}
this.name = name;
this.company = company;
this.expertise = expertise;
this.writeCode = function () {
console.log("Writing some public static thing..")
}
}
16.柯里化
var curry = function (fn) {
var limit = fn.length;
return function judgeCurry(...args) {
return function (...args) {
if (args.length >= limit) {
return fn.apply(null, args);
} else {
return function (...args2) {
return judgeCurry.apply(null, args.concat(args2))
}
}
}
}
};
var currySingle = fn => judgeCurry = (...args) => args.length >= fn.length ? fn.apply(null, args) : (...args2) => judgeCurry.apply(null, args.concat(args2));
17.对象拷贝与赋值
var obj = {
name: 'xiaoming',
age: 23
};
var newObj = obj;
newObj.name = 'xiaohua';
console.log(obj.name);//xiaohua
console.log(newObj.name);//xiaohua
我们将obj对象赋值给了newObj对象，从而改变newObj的name属性，但是obj对象的name属性也被篡改，这是因为实际上newObj对象获得的只是一个内存地址，而不是真正的拷贝，所以obj对象被篡改。
var obj = {
name: 'xiaoming',
age: 23
};
var newObj = Object.assign({}, obj, {color: 'blue'});
newObj.name = 'xiaohua';
console.log(obj.name);//xiaoming
console.log(newObj.name);//xiaohua
console.log(newObj.color);//blue
18.拷贝
利用Object.assign()方法进行对象的深拷贝可以避免源对象被篡改的可能。因为Object.assign()方法可以把任意多个的源对象自身的可枚举属性拷贝给目标对象，然后返回目标对象。
var obj = {
name: 'xiaoming',
age: 23
};
var newObj = Object.create(obj);
newObj.name = 'xiaohua';
console.log(obj.name);//xiaoming
console.log(newObj.name);//xiaohua
我们也可以使用Object.create()方法进行对象的拷贝，Object.create()方法可以创建一个具有指定原型对象和属性的新对象。
19.设置等高的列
<div class="equalHeight" style="border: 1px solid">
<p>First Line</p>
<p>Second Line</p>
<p>Third Line</p>
</div>
<div class="equalHeight" style="border: 1px solid">
<p>Column Two</p>
</div>
$(function () {
equalHeight(".equalHeight");
});
var maxHeight = 0;
function equalHeight(col) {
col = $(col);
col.each(function () {
if ($(this).height() > maxHeight) {
maxHeight = $(this).height()
}
});
col.height(maxHeight);
}
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