前端代碼集

zone 發(fā)布于2019-08-21 17:06 / 326人閱讀

摘要：閉包正是可以做到這一點(diǎn)，因?yàn)樗粫?huì)釋放外部的引用，從而函數(shù)內(nèi)部的值可以得以保留。利用方法進(jìn)行對(duì)象的深拷貝可以避免源對(duì)象被篡改的可能。我們也可以使用方法進(jìn)行對(duì)象的拷貝，方法可以創(chuàng)建一個(gè)具有指定原型對(duì)象和屬性的新對(duì)象。

HTML5

使用FileReader實(shí)現(xiàn)前端圖片預(yù)覽

獲取到頁(yè)面中所有的checkbox怎么做？(不使用第三方框架)

JavaScript模版引擎小實(shí)例

Javascript

實(shí)現(xiàn)JS函數(shù)重載

JS跨瀏覽器綁定事件函數(shù)

JS單體模式

使用prototype屬性定義的對(duì)象方法

閉包實(shí)現(xiàn)結(jié)果緩存

閉包實(shí)現(xiàn)封裝

閉包實(shí)現(xiàn)類和繼承

如何判斷某變量是否為數(shù)組數(shù)據(jù)類型？

Javascript繼承-借用構(gòu)造函數(shù)

Javascript原型-封裝

通過閉包修正函數(shù)的上下文（bind 瀏覽器不支持解決方案）

優(yōu)化JavaScript的構(gòu)造函數(shù)(new關(guān)鍵字的使用)

柯里化

對(duì)象拷貝與賦值

CSS

居中

菜單欄下拉

JQuery

JQ設(shè)置等高的列

HTML5 使用FileReader實(shí)現(xiàn)前端圖片預(yù)覽

數(shù)據(jù)

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);

JavaScript 實(shí)現(xiàn)JS函數(shù)重載

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"));

JS跨瀏覽器綁定事件函數(shù)

常規(guī)實(shí)現(xiàn)方法

//跨瀏覽器添加事件
function addHandler(target, eventType, handler) {
    //檢測(cè)瀏覽器類型，并且重寫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);
        }
    }

    //調(diào)用新的函數(shù)
    addHandler(target, eventType, handler);
}

//跨瀏覽器移除事件
function removeHandler(target, eventType, handler) {
    //檢測(cè)瀏覽器類型，并且重寫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);
}

優(yōu)化方法

//綁定事件
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);
    };

JS單體模式

var shoppingCar = (function () {
    //這個(gè)是由購(gòu)物車構(gòu)造器所創(chuàng)建的實(shí)例
    var instance;

    //購(gòu)物車的構(gòu)造器函數(shù)　
    function Trolley() {
        this.date = new Date().getDate();//實(shí)例屬性，當(dāng)前日期
    }

    //原型屬性，一個(gè)返回當(dāng)前日期的方法
    Trolley.prototype.getDate = function () {
        return this.date;
    };

    //暴露出去的公共API
    return function () {
        //如果實(shí)例不存在，那么就調(diào)用Trolley構(gòu)造器實(shí)例化一個(gè)
        if (!instance) {
            instance = new Trolley();
        }

        //將實(shí)例返回外部
        return instance;
    }
}());

var a = new shoppingCar();
var b = new shoppingCar();
console.log(a === b);//true

使用prototype屬性定義的對(duì)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屬性定義的對(duì)象方法，是靜態(tài)方法，只能直接用類名進(jìn)行調(diào)用！另外，此靜態(tài)方法中無(wú)法使用this變量來(lái)調(diào)用對(duì)象其他的屬性！
2、使用prototype屬性定義的對(duì)象方法，是非靜態(tài)方法，只有在實(shí)例化后才能使用！其方法內(nèi)部可以this來(lái)引用對(duì)象自身中的其他屬性！

閉包實(shí)現(xiàn)結(jié)果緩存

var CachedSearchBox = (function () {
    var cache = {},
        table = [];

    return {
        attachSearchBox: function (dsid) {
            if (dsid in cache) { //如果結(jié)果在緩存中
                return cache[dsid]; //直接返回緩存中的對(duì)象
            }
            var fsb = new uikit.webctrl.SearchBox(dsid);//新建
            cache[dsid] = fsb;//更新緩存
            if (count.length > 100) {
                delete cache[shift()];
            }
            return fsb;
        },

        clearSearchBox: function (dsid) {
            if (dsid in cache) {
                cache[dsid].clearSelection();
            }
        }
    }
})();

CachedSearchBox.attachSearchBox("input");

我們開發(fā)中會(huì)碰到很多情況，設(shè)想我們有一個(gè)處理過程很耗時(shí)的函數(shù)對(duì)象，每次調(diào)用都會(huì)花費(fèi)很長(zhǎng)時(shí)間，
那么我們就需要將計(jì)算出來(lái)的值存儲(chǔ)起來(lái)，當(dāng)調(diào)用這個(gè)函數(shù)的時(shí)候，首先在緩存中查找，如果找不到，則進(jìn)行計(jì)算，然后更新緩存并返回值，如果找到了，直接返回查找到的值即可。閉包正是可以做到這一點(diǎn)，因?yàn)樗粫?huì)釋放外部的引用，從而函數(shù)內(nèi)部的值可以得以保留。

閉包實(shí)現(xiàn)封裝

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

閉包實(shí)現(xiàn)類和繼承

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();//繼承自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

如何判斷某變量是否為數(shù)組數(shù)據(jù)類型

if (typeof Array.isArray === "undefined") {
    Array.isArray = function (arg) {
        return Object.prototype.toString.call(arg) === "[object Array]"
    };
}

Javascript繼承-借用構(gòu)造函數(shù)

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

Javascript原型-封裝

var Dialog = (function () {
    function Dialog() {
    }

    Dialog.prototype = {
        init: function () {
            console.log("ok");
        }
    };

    return Dialog;
}());

var d = new Dialog();
d.init();//ok

通過閉包修正函數(shù)的上下文（瀏覽器不支持解決方案）

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));
        }
    }
}

優(yōu)化JavaScript的構(gòu)造函數(shù)(new關(guān)鍵字的使用)

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..")
    }
}

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));

對(duì)象拷貝與賦值

var obj = {
    name: "xiaoming",
    age: 23
};
var newObj = obj;
newObj.name = "xiaohua";
console.log(obj.name);//xiaohua
console.log(newObj.name);//xiaohua

我們將obj對(duì)象賦值給了newObj對(duì)象，從而改變newObj的name屬性，但是obj對(duì)象的name屬性也被篡改，這是因?yàn)閷?shí)際上newObj對(duì)象獲得的只是一個(gè)內(nèi)存地址，而不是真正的拷貝，所以obj對(duì)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

利用Object.assign()方法進(jìn)行對(duì)象的深拷貝可以避免源對(duì)象被篡改的可能。因?yàn)?b>Object.assign()方法可以把任意多個(gè)的源對(duì)象自身的可枚舉屬性拷貝給目標(biāo)對(duì)象，然后返回目標(biāo)對(duì)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

我們也可以使用Object.create()方法進(jìn)行對(duì)象的拷貝，Object.create()方法可以創(chuàng)建一個(gè)具有指定原型對(duì)象和屬性的新對(duì)象。

CSS 居中

#main {
    width: 440px;
    margin: 0 auto;
    position: relative;
    text-align: center;
}

菜單欄下拉

.menu > li {
    display: block;
    float: left;
    position: relative;
}

JQuery JQ設(shè)置等高的列


    First Line
    Second Line
    Third Line


    Column Two

$(function () {
    equalHeight(".equalHeight");
});

var maxHeight = 0;

function equalHeight(col) {
    col = $(col);
    col.each(function () {
        if ($(this).height() > maxHeight) {
            maxHeight = $(this).height()
        }
    });
    col.height(maxHeight);
}