生成器和迭代器(仅适用于Firefox 2+和Safari)。

function fib() {
  var i = 0, j = 1;
  while (true) {
    yield i;
    var t = i;
    i = j;
    j += t;
  }
}

var g = fib();
for (var i = 0; i < 10; i++) {
  document.write(g.next() + "<br>\n");
}

The function containing the yield keyword is a generator. When you call it, its formal parameters are bound to actual arguments, but its body isn't actually evaluated. Instead, a generator-iterator is returned. Each call to the generator-iterator's next() method performs another pass through the iterative algorithm. Each step's value is the value specified by the yield keyword. Think of yield as the generator-iterator version of return, indicating the boundary between each iteration of the algorithm. Each time you call next(), the generator code resumes from the statement following the yield. In normal usage, iterator objects are "invisible"; you won't need to operate on them explicitly, but will instead use JavaScript's for...in and for each...in statements to loop naturally over the keys and/or values of objects.

var objectWithIterator = getObjectSomehow();

for (var i in objectWithIterator)
{
  document.write(objectWithIterator[i] + "<br>\n");
}

你可以在任何对象上执行一个对象的方法，不管它是否有这个方法。当然，它可能并不总是有效(如果方法假设对象具有它没有的东西)，但它可能非常有用。例如:

function(){
    arguments.push('foo') // This errors, arguments is not a proper array and has no push method
    Array.prototype.push.apply(arguments, ['foo']) // Works!
}

模块模式

<script type="text/javascript">
(function() {

function init() {
  // ...
}

window.onload = init;
})();
</script>

没有使用var语句或在函数外部声明的变量和函数将在全局作用域中定义。如果一个同名的变量/函数已经存在，它将被无声地覆盖，这可能导致很难发现错误。一种常见的解决方案是将整个代码体封装到一个匿名函数中并立即执行它。这样，所有变量/函数都定义在匿名函数的作用域中，不会泄漏到全局作用域中。

要显式地在全局作用域定义一个变量/函数，它们必须以window为前缀:

window.GLOBAL_VAR = 12;
window.global_function = function() {};

您还可以使用前面提到的原型链spoon16扩展(继承)类和重写属性/方法。

在下面的例子中，我们创建了一个类Pet并定义了一些属性。我们还重写了继承自Object的. tostring()方法。

在此之后，我们创建了一个Dog类，它扩展了Pet并重写了. tostring()方法，再次改变了它的行为(多态性)。此外，我们还向子类添加了一些其他属性。

在此之后，我们检查继承链以显示Dog仍然是Dog类型、Pet类型和Object类型。

// Defines a Pet class constructor 
function Pet(name) 
{
    this.getName = function() { return name; };
    this.setName = function(newName) { name = newName; };
}

// Adds the Pet.toString() function for all Pet objects
Pet.prototype.toString = function() 
{
    return 'This pets name is: ' + this.getName();
};
// end of class Pet

// Define Dog class constructor (Dog : Pet) 
function Dog(name, breed) 
{
    // think Dog : base(name) 
    Pet.call(this, name);
    this.getBreed = function() { return breed; };
}

// this makes Dog.prototype inherit from Pet.prototype
Dog.prototype = new Pet();

// Currently Pet.prototype.constructor
// points to Pet. We want our Dog instances'
// constructor to point to Dog.
Dog.prototype.constructor = Dog;

// Now we override Pet.prototype.toString
Dog.prototype.toString = function() 
{
    return 'This dogs name is: ' + this.getName() + 
        ', and its breed is: ' + this.getBreed();
};
// end of class Dog

var parrotty = new Pet('Parrotty the Parrot');
var dog = new Dog('Buddy', 'Great Dane');
// test the new toString()
alert(parrotty);
alert(dog);

// Testing instanceof (similar to the `is` operator)
alert('Is dog instance of Dog? ' + (dog instanceof Dog)); //true
alert('Is dog instance of Pet? ' + (dog instanceof Pet)); //true
alert('Is dog instance of Object? ' + (dog instanceof Object)); //true

这个问题的两个答案都是从Ray Djajadinata的一篇很棒的MSDN文章中修改的代码。

您不需要为函数定义任何参数。你可以使用函数的参数数组类对象。

function sum() {
    var retval = 0;
    for (var i = 0, len = arguments.length; i < len; ++i) {
        retval += arguments[i];
    }
    return retval;
}

sum(1, 2, 3) // returns 6

私有方法

对象可以有私有方法。

function Person(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;

    // A private method only visible from within this constructor
    function calcFullName() {
       return firstName + " " + lastName;    
    }

    // A public method available to everyone
    this.sayHello = function () {
        alert(calcFullName());
    }
}

//Usage:
var person1 = new Person("Bob", "Loblaw");
person1.sayHello();

// This fails since the method is not visible from this scope
alert(person1.calcFullName());