HTML5

使用FileReader實作前端圖片預覽

<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);

取到頁面中所有的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]);
    }
}

JavaScript模版引擎小實體

<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>

資料

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

實作JS函式多載

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跨瀏覽器系結事件函式

常規實作方法

//跨瀏覽器添加事件
function addHandler(target, eventType, handler) {
    //檢測瀏覽器型別，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);
        }
    }
    //呼叫新的函式
    addHandler(target, eventType, handler);
}
//跨瀏覽器移除事件
function removeHandler(target, eventType, handler) {
    //檢測瀏覽器型別，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);
}

優化方法

//系結事件
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 () {
    //這個是由購物車構造器所創建的實體
    var instance;
    //購物車的構造器函式　
    function Trolley() {
        this.date = new Date().getDate();//實體屬性，當前日期
    }
    //原型屬性，一個回傳當前日期的方法
    Trolley.prototype.getDate = function () {
        return this.date;
    };
    //暴露出去的公共API
    return function () {
        //如果實體不存在，那么就呼叫Trolley構造器實體化一個
        if (!instance) {
            instance = new Trolley();
        }
        //將實體回傳外部
        return instance;
    }
}());
var a = new shoppingCar();
var b = new shoppingCar();
console.log(a === b);//true

使用prototype屬性定義的物件方法

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屬性定義的物件方法，是靜態方法，只能直接用類名進行呼叫！另外，此靜態方法中無法使用this變數來呼叫物件其他的屬性！
2、使用prototype屬性定義的物件方法，是非靜態方法，只有在實體化后才能使用！其方法內部可以this來參考物件自身中的其他屬性！

閉包實作結果快取

var CachedSearchBox = (function () {
    var cache = {},
        table = [];
    return {
        attachSearchBox: function (dsid) {
            if (dsid in cache) { //如果結果在快取中
                return cache[dsid]; //直接回傳快取中的物件
            }
            var fsb = new uikit.webctrl.SearchBox(dsid);//新建
            cache[dsid] = fsb;//更新快取
            if (count.length > 100) {
                delete cache[shift()];
            }
            return fsb;
        },
        clearSearchBox: function (dsid) {
            if (dsid in cache) {
                cache[dsid].clearSelection();
            }
        }
    }
})();
CachedSearchBox.attachSearchBox('input');

我們開發中會碰到很多情況，設想我們有一個處理程序很耗時的函式物件，每次呼叫都會花費很長時間，

那么我們就需要將計算出來的值存盤起來，當呼叫這個函式的時候，首先在快取中查找，如果找不到，則進行計算，然后更新快取并回傳值，如果找到了，直接回傳查找到的值即可，閉包正是可以做到這一點，因為它不會釋放外部的參考，從而函式內部的值可以得以保留，

閉包實作封裝

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

閉包實作類和繼承

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

如何判斷某變數是否為陣列資料型別

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

Javascript繼承-借用建構式

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

通過閉包修正函式的背景關系（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));
        }
    }
}

優化JavaScript的建構式(new關鍵字的使用)

// 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));

物件拷貝與賦值

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物件賦值給了newObj物件，從而改變newObj的name屬性，但是obj物件的name屬性也被篡改，這是因為實際上newObj物件獲得的只是一個記憶體地址，而不是真正的拷貝，所以obj物件被篡改，

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()**方法進行物件的

深拷貝

可以避免源物件被篡改的可能，因為Object.assign()方法可以把任意多個的源物件自身的可列舉屬性拷貝給目標物件，然后回傳目標物件，

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()**方法進行物件的拷貝，Object.create()方法可以創建一個具有指定原型物件和屬性的新物件，

CSS

居中

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

選單欄下拉

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

JQuery

Q設定等高的列

<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);
}

轉載請註明出處，本文鏈接：https://www.uj5u.com/qianduan/236606.html

標籤：其他

上一篇：HTML+CSS仿BMW官網

下一篇：Ant Design Vue生成動態選單a-menu

前端代碼合集