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## 你可能不知道的10 个JavaScript 小技巧[转]

##### 1.变量转换

 var myVar = "3.14159", str = ""+ myVar,// to string int = ~~myVar, // to integer float = 1*myVar, // to float bool = !!myVar, /* to boolean - any string with length and any number except 0 are true */ array = [myVar]; // to array

##### 2.十进制转换为十六进制或者八进制，或者反过来

 (int).toString(16); // converts int to hex, eg 12 => "C" (int).toString(8); // converts int to octal, eg. 12 => "14" parseInt(string,16) // converts hex to int, eg. "FF" => 255 parseInt(string,8) // converts octal to int, eg. "20" => 16

##### 3.玩转数字

 0xFF; // Hex declaration, returns 255 020; // Octal declaration, returns 16 1e3; // Exponential, same as 1 * Math.pow(10,3), returns 1000 (1000).toExponential(); // Opposite with previous, returns 1e3 (3.1415).toFixed(3); // Rounding the number, returns "3.142"

##### 4.Javascript 版本检测

 var JS_ver = []; (Number.prototype.toFixed)?JS_ver.push("1.5"):false; ([].indexOf && [].forEach)?JS_ver.push("1.6"):false; ((function(){try {[a,b] = [0,1];return true;}catch(ex) {return false;}})())?JS_ver.push("1.7"):false; ([].reduce && [].reduceRight && JSON)?JS_ver.push("1.8"):false; ("".trimLeft)?JS_ver.push("1.8.1"):false; JS_ver.supports = function() { if (arguments[0]) return (!!~this.join().indexOf(arguments[0] +",") +","); else return (this[this.length-1]); } alert("Latest Javascript version supported: "+ JS_ver.supports()); alert("Support for version 1.7 : "+ JS_ver.supports("1.7"));

##### 6.判断属性是否存在

 // BAD: This will cause an error in code when foo is undefined if (foo) { doSomething(); } // GOOD: This doesn't cause any errors. However, even when // foo is set to NULL or false, the condition validates as true if (typeof foo != "undefined") { doSomething(); } // BETTER: This doesn't cause any errors and in addition // values NULL or false won't validate as true if (window.foo) { doSomething(); }

 // UGLY: we have to proof existence of every // object before we can be sure property actually exists if (window.oFoo && oFoo.oBar && oFoo.oBar.baz) { doSomething(); }

##### 7.给函数传递参数

 function doSomething(arg0, arg1, arg2, arg3, arg4) { ... } doSomething('', 'foo', 5, [], false);

 function doSomething() { // Leaves the function if nothing is passed if (!arguments[0]) { return false; } var oArgs = arguments[0] arg0 = oArgs.arg0 || "", arg1 = oArgs.arg1 || "", arg2 = oArgs.arg2 || 0, arg3 = oArgs.arg3 || [], arg4 = oArgs.arg4 || false; } doSomething({ arg1 : "foo", arg2 : 5, arg4 : false });

##### 8.使用document.createDocumentFragment( )

 function createList() { var aLI = ["first item", "second item", "third item", "fourth item", "fith item"]; // Creates the fragment var oFrag = document.createDocumentFragment(); while (aLI.length) { var oLI = document.createElement("li"); // Removes the first item from array and appends it // as a text node to LI element oLI.appendChild(document.createTextNode(aLI.shift())); oFrag.appendChild(oLI); } document.getElementById('myUL').appendChild(oFrag); }

##### 9.为replace()方法传递一个函数

 var sFlop = "Flop: [Ah] [Ks] [7c]"; var aValues = {"A":"Ace","K":"King",7:"Seven"}; var aSuits = {"h":"Hearts","s":"Spades", "d":"Diamonds","c":"Clubs"}; sFlop = sFlop.replace(/\[\w+\]/gi, function(match) { match = match.replace(match[2], aSuits[match[2]]); match = match.replace(match[1], aValues[match[1]] +" of "); return match; }); // string sFlop now contains: // "Flop: [Ace of Hearts] [King of Spades] [Seven of Clubs]"

##### 10.循环中标签的使用

 outerloop: for (var iI=0;iI<5;iI++) { if (somethingIsTrue()) { // Breaks the outer loop iteration break outerloop; } innerloop: for (var iA=0;iA<5;iA++) { if (somethingelseIsTrue()) { // Breaks the inner loop iteration break innerloop; } } }

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