那些年，收集的javascript代码（一）

一、取URL中的参数

function getParameterByName(name) { var match = RegExp(‘[?&]’ + name + ‘=([^&]*)’) .exec(window.location.search); return match && decodeURIComponent(match[1].replace(/+/g, ‘ ‘)); }

二、正则分组

var testStr="<div><img src='/a.jpg' alt='' /><span>test<img src='/b.jpg' alt='' /><span>TTest<img src='/c.png' alt='' /></div>";
var reg=/<img\ssrc='(.*?)'\s+alt=''\s*\/>/g;
var match=reg.exec(testStr),results=[];
while(match != null){
    results.push(match[1]);
    match=reg.exec(testStr);
}
console.log(results);
/*
Array ["/a.jpg", "/b.jpg", "/c.png"]
*/

三、为什么parseInt(1/0,19)的结果为18

1/0的结果是Infinity，所以parseInt(1/0,19)等同于parseInt(“Infinity”,19)，而在19进制中：

 19进制       10进制
--------------------
   0            0
   1            1
   2            2
   3            3
   4            4
   5            5
   6            6
   7            7
   8            8
   9            9
   a            10
   b            11
   c            12
   d            13
   e            14
   f             15
   g            16
   h            17
   i             18

i表示18，所以parseInt(1/0,19)的结果为18。

四、jQuery中获取设置checkbox选中状态

由于在jQuery1.6以后.attr(“checked”)的返回结果是 checked，所以一般用下面两种方法获取选中状态：

$("#checkboxID").is(":checked");
//jQuery 1.6 +
$("#checkboxID").prop("checked");

选中checkbox

一个简单的示例：

//jQuery 1.6+
$("#checkboxID").prop("checked", true);
$("#checkboxID").prop("checked", false);

//jQuery 1.5 and below
$('#checkboxID').attr('checked','checked')
$('#checkboxID').removeAttr('checked')

五、jQuery中判断一个元素是否存在

if ($(selector).length)

六、用JavaScript对URL进行编码

var myUrl = "http://example.com/index.html?param=1&amp;anotherParam=2";
var myOtherUrl = "http://example.com/index.html?url=" + encodeURIComponent(myUrl);

七、jQuery中event.preventDefault() 与 return false 的区别

//Demo1 event.preventDefault()
$('a').click(function (e) {
    // custom handling here

    e.preventDefault();
});

//Demo2 return false
$('a').click(function () {
    // custom handling here

    return false;
};

jQuery中return false相当于同时调用e.preventDefault 和 e.stopPropagation。要注意的是，在原生js中，return false仅仅相当于调用了e.preventDefault。

八、JavaScript检查一个字符串是否为空最简单的方法

if (strValue) {
    //do something
}

九、用JavaScript添加和删除class

//Add Class
document.getElementById("MyElement").className += " MyClass";

//Remove Class
document.getElementById("MyElement").className = document.getElementById("MyElement").className.replace(/(?:^|\s)MyClass(?!\S)/,'');

十、在jQuery中取消一个ajax请求

var xhr = $.ajax({
    type: "POST",
    url: "test.php",
    data: "name=test",
    success: function(msg){
       alert( msg );
    }
});

//取消请求
xhr.abort()

十一、JavaScript删除数组中的项 delete vs splice

var myArray=["a","b","c"];
delete myArray[0];
for(var i=0,j=myArray.length;i<j;i++){
    console.log(myArray[i]);
    /*
    undefined
    b
    c
    */
}

var myArray2=["a","b","c"];
myArray2.splice(0,1);
for(var i=0,j=myArray2.length;i<j;i++){
    console.log(myArray2[i]);
    /*
    b
    c
    */
}

上面的代码已经说明区别了，一个是设置为undefined，一个是真正的删除了。

十二、JavaScript中16进制与10进制相互转换

var sHex=(255).toString(16);//ff
var iNum=parseInt("ff",16);//255

十三、JavaScript多行字符串

如何在JavaScript中方便地写一个多行字符串呢，有三种方案，你自己选吧：

//one
var testHtml="a"+"b"+"c";

//two
var testHtml2="a\b\c";

//three
var testHtml3=["a","b","c"].join("");

十四、JavaScript中!!操作符是什么

console.log(!!10);//true
console.log(!!0);//false
console.log(!!"abc");//true
console.log(!!"");//false

简单地说就是把右侧的值转为bool值

十五、JavaScript实现endsWith

String.prototype.endsWith = function(suffix) {
    return this.indexOf(suffix, this.length - suffix.length) !== -1;
};

//or
function endsWith(str, suffix) {
    return str.indexOf(suffix, str.length - suffix.length) !== -1;
}

十六、JavaScript中克隆对象

function clone(obj) {
    // Handle the 3 simple types, and null or undefined
    if (null == obj || "object" != typeof obj) return obj;

    // Handle Date
    if (obj instanceof Date) {
        var copy = new Date();
        copy.setTime(obj.getTime());
        return copy;
    }

    // Handle Array
    if (obj instanceof Array) {
        var copy = [];
        for (var i = 0, var len = obj.length; i < len; ++i) {
            copy[i] = clone(obj[i]);
        }
        return copy;
    }

    // Handle Object
    if (obj instanceof Object) {
        var copy = {};
        for (var attr in obj) {
            if (obj.hasOwnProperty(attr)) copy[attr] = clone(obj[attr]);
        }
        return copy;
    }

    throw new Error("Unable to copy obj! Its type isn't supported.");
}

十七、JavaScript字符与ASCII码间的转换

console.log("\n".charCodeAt(0));//10
console.log(String.fromCharCode(65));//A

十八、JavaScript中浮点数的相等判断不能用 ==

console.log(0.1+0.2 == 0.3);//false
console.log(Math.abs(0.1+0.2 - 0.3) < 0.000001);//true

如上所示，浮点数相等判断要用差的绝对值小于某一个数来判断。至于原因可以参考这里：http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

十九、JavaScript中base64编码

var Base64 = {
// private property
_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",

// public method for encoding
encode : function (input) {
    var output = "";
    var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
    var i = 0;

    input = Base64._utf8_encode(input);

    while (i < input.length) {

        chr1 = input.charCodeAt(i++);
        chr2 = input.charCodeAt(i++);
        chr3 = input.charCodeAt(i++);

        enc1 = chr1 >> 2;
        enc2 = ((chr1 &amp; 3) << 4) | (chr2 >> 4);
        enc3 = ((chr2 &amp; 15) << 2) | (chr3 >> 6);
        enc4 = chr3 &amp; 63;

        if (isNaN(chr2)) {
            enc3 = enc4 = 64;
        } else if (isNaN(chr3)) {
            enc4 = 64;
        }

        output = output +
        this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
        this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);

    }

    return output;
},

// public method for decoding
decode : function (input) {
    var output = "";
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;

    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

    while (i < input.length) {

        enc1 = this._keyStr.indexOf(input.charAt(i++));
        enc2 = this._keyStr.indexOf(input.charAt(i++));
        enc3 = this._keyStr.indexOf(input.charAt(i++));
        enc4 = this._keyStr.indexOf(input.charAt(i++));

        chr1 = (enc1 << 2) | (enc2 >> 4);
        chr2 = ((enc2 &amp; 15) << 4) | (enc3 >> 2);
        chr3 = ((enc3 &amp; 3) << 6) | enc4;

        output = output + String.fromCharCode(chr1);

        if (enc3 != 64) {
            output = output + String.fromCharCode(chr2);
        }
        if (enc4 != 64) {
            output = output + String.fromCharCode(chr3);
        }

    }

    output = Base64._utf8_decode(output);

    return output;

},

// private method for UTF-8 encoding
_utf8_encode : function (string) {
    string = string.replace(/\r\n/g,"\n");
    var utftext = "";

    for (var n = 0; n < string.length; n++) {

        var c = string.charCodeAt(n);

        if (c < 128) {
            utftext += String.fromCharCode(c);
        }
        else if((c > 127) &amp;&amp; (c < 2048)) {
            utftext += String.fromCharCode((c >> 6) | 192);
            utftext += String.fromCharCode((c &amp; 63) | 128);
        }
        else {
            utftext += String.fromCharCode((c >> 12) | 224);
            utftext += String.fromCharCode(((c >> 6) &amp; 63) | 128);
            utftext += String.fromCharCode((c &amp; 63) | 128);
        }

    }

    return utftext;
},

// private method for UTF-8 decoding
_utf8_decode : function (utftext) {
    var string = "";
    var i = 0;
    var c = c1 = c2 = 0;

    while ( i < utftext.length ) {

        c = utftext.charCodeAt(i);

        if (c < 128) {
            string += String.fromCharCode(c);
            i++;
        }
        else if((c > 191) &amp;&amp; (c < 224)) {
            c2 = utftext.charCodeAt(i+1);
            string += String.fromCharCode(((c &amp; 31) << 6) | (c2 &amp; 63));
            i += 2;
        }
        else {
            c2 = utftext.charCodeAt(i+1);
            c3 = utftext.charCodeAt(i+2);
            string += String.fromCharCode(((c &amp; 15) << 12) | ((c2 &amp; 63) << 6) | (c3 &amp; 63));
            i += 3;
        }

    }

    return string;
}
}

//encode
Base64.encode("Test"); //VGVzdA==

//decode
Base64.decode("VGVzdA=="); // Test

二十、jQuery中each跟map的区别

each跟map都可以用来遍历Array或Object，区别是each不改变原来的Array或Object，map是操作给定的Array或Object返回一个新Array或Object。Demo:

var items = [1,2,3,4];
$.each(items, function() {
  alert('this is ' + this);//alert 1,2,3,4
});
var newItems = $.map(items, function(i) {
  return i + 1;
});
// newItems is [2,3,4,5]

map会占用更多的内存，所以如果只是遍历建议用each。

二十一、判断一个对象是否为数组

function isArray(obj){
    return Object.prototype.toString.call(obj) == "[object Array]";
}

不能用instanceof 和 constructor来判断，原因参考：http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/

二十二、通过原型继承创建一个新对象

function inherit(p){
    if(!p){
        throw TypeError("p is not an object or null");
    }
    if(Object.create){
        return Object.create(p);
    }
    var t=typeof p;
    if(t !== "object" &amp;&amp; t !== "function"){
        throw TypeError("p is not an object or null");
    }
    function f(){};
    f.prototype=p;
    return new f();
}

注意：这种方法不能处理参数为null的情况。转自：http://www.cnblogs.com/jscode/archive/2012/07/25/2605395.html