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。

函数在JavaScript中是第一类公民:

var passFunAndApply = function (fn,x,y,z) { return fn(x,y,z); };

var sum = function(x,y,z) {
  return x+y+z;
};

alert( passFunAndApply(sum,3,4,5) ); // 12

函数式编程技术可以用来编写优雅的javascript。

特别是，函数可以作为参数传递，例如Array.filter()接受回调:

[1, 2, -1].filter(function(element, index, array) { return element > 0 });
// -> [1,2]

你也可以声明一个“private”函数，它只存在于特定函数的作用域中:

function PrintName() {
    var privateFunction = function() { return "Steve"; };
    return privateFunction();
}

JavaScript中的时间戳:

// Usual Way
var d = new Date();
timestamp = d.getTime();

// Shorter Way
timestamp = (new Date()).getTime();

// Shortest Way
timestamp = +new Date();

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");
}

当使用console.log()用于Firebug时，防止在Internet Explorer中测试时出现恼人的错误:

function log(message) {
    (console || { log: function(s) { alert(s); }).log(message);
}

知道一个函数需要多少个参数

function add_nums(num1, num2, num3 ){
    return num1 + num2 + num3;
}
add_nums.length // 3 is the number of parameters expected.

知道函数接收了多少参数

function add_many_nums(){
    return arguments.length;
}    
add_many_nums(2,1,122,12,21,89); //returns 6