【转】 这些年,我收集的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</span><img src='/b.jpg' alt='' /><span>TTest</span><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:
//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&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()
要注意的是,在ajax请求未响应之前可以用xhr.abort()取消,但如果请求已经到达了服务器端,这样做的结果仅仅是让浏览器不再监听这个请求的响应,但服务器端仍然会进行处理。
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 & 3) << 4) | (chr2 >> 4); enc3 = ((chr2 & 15) << 2) | (chr3 >> 6); enc4 = chr3 & 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 & 15) << 4) | (enc3 >> 2); chr3 = ((enc3 & 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) && (c < 2048)) { utftext += String.fromCharCode((c >> 6) | 192); utftext += String.fromCharCode((c & 63) | 128); } else { utftext += String.fromCharCode((c >> 12) | 224); utftext += String.fromCharCode(((c >> 6) & 63) | 128); utftext += String.fromCharCode((c & 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) && (c < 224)) { c2 = utftext.charCodeAt(i+1); string += String.fromCharCode(((c & 31) << 6) | (c2 & 63)); i += 2; } else { c2 = utftext.charCodeAt(i+1); c3 = utftext.charCodeAt(i+2); string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 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" && 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。