原型继承(由Douglas Crockford推广)彻底改变了在Javascript中思考负载的方式。

Object.beget = (function(Function){
    return function(Object){
        Function.prototype = Object;
        return new Function;
    }
})(function(){});

这是一个杀手!可惜几乎没有人使用它。

它允许你“生成”任何对象的新实例，扩展它们，同时保持一个(活的)原型继承链接到它们的其他属性。例子:

var A = {
  foo : 'greetings'
};  
var B = Object.beget(A);

alert(B.foo);     // 'greetings'

// changes and additionns to A are reflected in B
A.foo = 'hello';
alert(B.foo);     // 'hello'

A.bar = 'world';
alert(B.bar);     // 'world'


// ...but not the other way around
B.foo = 'wazzap';
alert(A.foo);     // 'hello'

B.bar = 'universe';
alert(A.bar);     // 'world'

你永远不需要使用eval()来组装全局变量名。

也就是说，如果你有几个名为spec_grapes, spec_apples的全局变量(无论出于什么原因)，你不需要用eval("spec_" + var)访问它们。

所有全局变量都是window[]的成员，所以你可以执行window["spec_" + var]。

如果你盲目地eval()一个JSON字符串来反序列化它，你可能会遇到问题:

这并不安全。该字符串可能包含恶意函数调用! 如果你没有将JSON字符串括在括号中，属性名可能会被误认为是标签，导致意外的行为或语法错误: Eval ("{\"foo\": 42}");//语法错误:无效标签 Eval ("({\"foo\": 42})");/ /好吧

“JavaScript中的扩展方法”通过prototype属性。

Array.prototype.contains = function(value) {  
    for (var i = 0; i < this.length; i++) {  
        if (this[i] == value) return true;  
    }  
    return false;  
}

这将为所有Array对象添加一个contains方法。您可以使用以下语法调用此方法

var stringArray = ["foo", "bar", "foobar"];
stringArray.contains("foobar");

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!
}

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");
}