分享经典的JavaScript开发技巧

function Person(firstName, lastName){ this.firstName = firstName; this.lastName = lastName;}var Saad = new Person("Saad", "Mousliki");

var arr = ["a", "b", "c"];typeof arr; // 返回 "object" arr instanceof Array // truearr.constructor(); //[]

(function(){ // 置于此处的代码将自动执行})(); (function(a,b){ var result = a+b; return result;})(10,20)

var items = [12, 548 , 'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' , 2145 , 119];var randomItem = items[Math.floor(Math.random() * items.length)];

var numbersArray = [] , max = 100;for( var i=1; numbersArray.push(i++) < max;); // numbers = [1,2,3 ... 100]

function generateRandomAlphaNum(len) { var rdmString = ""; for( ; rdmString.length < len; rdmString += Math.random().toString(36).substr(2)); return rdmString.substr(0, len);}

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411];numbers = numbers.sort(function(){ return Math.random() - 0.5});/* numbers 数组将类似于 [120, 5, 228, -215, 400, 458, -85411, 122205] */

var array1 = [12 , "foo" , {name "Joe"} , -2458];var array2 = ["Doe" , 555 , 100];Array.prototype.push.apply(array1, array2);/* array1 值为 [12 , "foo" , {name "Joe"} , -2458 , "Doe" , 555 , 100] */

function isNumber(n){ return !isNaN(parseFloat(n)) && isFinite(n);}

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

var myFrame = document.createElement('iframe');document.body.appendChild(myFrame);var myArray = window.frames[window.frames.length-1].Array;var arr = new myArray(a,b,10); // [a,b,10] // myArray 的构造器已经丢失，instanceof 的结果将不正常// 构造器是不能跨 frame 共享的arr instanceof Array; // false

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411]; var maxInNumbers = Math.max.apply(Math, numbers); var minInNumbers = Math.min.apply(Math, numbers);

var myArray = [12 , 222 , 1000 ]; myArray.length = 0; // myArray will be equal to [].

var items = [12, 548 ,'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' ,2154 , 119 ]; items.length; // return 11 delete items[3]; // return true items.length; // return 11 /* items 结果为 [12, 548, "a", undefined × 1, 5478, "foo", 8852, undefined × 1, "Doe", 2154, 119] */

var items = [12, 548 ,'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' ,2154 , 119 ]; items.length; // return 11 items.splice(3,1) ; items.length; // return 10 /* items 结果为 [12, 548, "a", 5478, "foo", 8852, undefined × 1, "Doe", 2154, 119]

var myArray = [12 , 222 , 1000 , 124 , 98 , 10 ]; myArray.length = 4; // myArray will be equal to [12 , 222 , 1000 , 124].

myArray.length = 10; // the new array length is 10 myArray[myArray.length - 1] ; // undefined

var foo = 10; foo == 10 && doSomething(); // is the same thing as if (foo == 10) doSomething(); foo == 5 || doSomething(); // is the same thing as if (foo != 5) doSomething();

function doSomething(arg1){  arg1 = arg1 || 10; // arg1 will have 10 as a default value if it's not already set}

var squares = [1,2,3,4].map(function (val) {  return val * val; }); // squares will be equal to [1, 4, 9, 16]

var num =2.443242342;num = num.toFixed(4); // num will be equal to 2.4432

for (var name in object) {  if (object.hasOwnProperty(name)) {   // do something with name } }

var a = 0; var b = ( a++, 99 ); console.log(a); // a will be equal to 1 console.log(b); // b is equal to 99

var navright = document.querySelector('#right'); var navleft = document.querySelector('#left'); var navup = document.querySelector('#up'); var navdown = document.querySelector('#down');

isFinite(0/0) ; // falseisFinite("foo"); // falseisFinite("10"); // trueisFinite(10); // trueisFinite(undefined); // falseisFinite(); // falseisFinite(null); // true，这点当特别注意

var numbersArray = [1,2,3,4,5]; var from = numbersArray.indexOf("foo") ; // from is equal to -1 numbersArray.splice(from,2); // will return [5]

var person = {name :'Saad', age : 26, department : {ID : 15, name : "R&D"} };var stringFromPerson = JSON.stringify(person);/* stringFromPerson 结果为 "{"name":"Saad","age":26,"department":{"ID":15,"name":"R&D"}}" */var personFromString = JSON.parse(stringFromPerson);/* personFromString 的值与 person 对象相同 */

var func1 = new Function(functionCode);var func2 = eval(functionCode);

var sum = 0; for (var i in arrayNumbers) {  sum += arrayNumbers[i]; }

var sum = 0; for (var i = 0, len = arrayNumbers.length; i < len; i++) {  sum += arrayNumbers[i]; }

setInterval('doSomethingPeriodically()', 1000); setTimeout('doSomethingAfterFiveSeconds()', 5000);

setInterval(doSomethingPeriodically, 1000); setTimeout(doSomethingAfterFiveSeconds, 5000);

function getCategory(age) {  var category = "";  switch (true) {   case isNaN(age):    category = "not an age";    break;   case (age >= 50):    category = "Old";    break;   case (age <= 20):    category = "Baby";    break;   default:    category = "Young";    break;  };  return category; } getCategory(5); // 将返回 "Baby"

function clone(object) {  function OneShotConstructor(){};  OneShotConstructor.prototype = object;  return new OneShotConstructor(); } clone(Array).prototype ; // []

function escapeHTML(text) {  var replacements= {"<": "<", ">": ">","&": "&", "/"": """};       return text.replace(/[<>&"]/g, function(character) {   return replacements[character];  }); }

var object = ['foo', 'bar'], i; for (i = 0, len = object.length; i <len; i++) {  try {   // do something that throws an exception  }  catch (e) {   // handle exception  } }

var object = ['foo', 'bar'], i; try {  for (i = 0, len = object.length; i <len; i++) {   // do something that throws an exception  } } catch (e) {  // handle exception }

var xhr = new XMLHttpRequest (); xhr.onreadystatechange = function () {  if (this.readyState == 4) {   clearTimeout(timeout);   // do something with response data  } } var timeout = setTimeout( function () {  xhr.abort(); // call error callback }, 60*1000 /* timeout after a minute */ ); xhr.open('GET', url, true); xhr.send();

var timerID = 0; function keepAlive() {  var timeout = 15000;  if (webSocket.readyState == webSocket.OPEN) {   webSocket.send('');  }  timerId = setTimeout(keepAlive, timeout); } function cancelKeepAlive() {  if (timerId) {   cancelTimeout(timerId);  } }