前端常用代码合集

JavaScript/前端
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2022-05-02
Chrome开发者工具Debug入门
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标签   JavaScript进阶

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);
}

前端常用代码合集

Chrome开发者工具Debug入门
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echarts实现可自定义配色中国地图省份选择效果
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