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());

Function.toString()(隐性):

function x() {
    alert("Hello World");
}
eval ("x = " + (x + "").replace(
    'Hello World',
    'STACK OVERFLOW BWAHAHA"); x("'));
x();

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'

方法(或函数)可以在不是它们设计使用的类型的对象上调用。这对于在自定义对象上调用本机(快速)方法非常有用。

var listNodes = document.getElementsByTagName('a');
listNodes.sort(function(a, b){ ... });

这段代码崩溃是因为listNodes不是数组

Array.prototype.sort.apply(listNodes, [function(a, b){ ... }]);

这段代码之所以有效，是因为listNodes定义了足够多的类数组属性(length，[]运算符)供sort()使用。

let.

与var缺乏块作用域对应的是let，在JavaScript 1.7中引入。

The let statement provides a way to associate values with variables within the scope of a block, without affecting the values of like-named variables outside the block. The let expression lets you establish variables scoped only to a single expression. The let definition defines variables whose scope is constrained to the block in which they're defined. This syntax is very much like the syntax used for var. You can also use let to establish variables that exist only within the context of a for loop.

  function varTest() {
        var x = 31;
    if (true) {
      var x = 71;  // same variable!
      alert(x);  // 71
    }
    alert(x);  // 71
  }

  function letTest() {
    let x = 31;
    if (true) {
      let x = 71;  // different variable
      alert(x);  // 71
    }
    alert(x);  // 31
  }

截至2008年，FireFox 2.0+和Safari 3.x支持JavaScript 1.7。

也许对某些人来说有点明显…

安装Firebug并使用console.log("hello")。这比使用随机alert();好多了，我记得几年前我经常这样做。