Javascript中的所有对象都实现为哈希表，因此它们的属性可以通过索引器访问，反之亦然。此外，你可以使用for/in操作符枚举所有属性:

var x = {a: 0};
x["a"]; //returns 0

x["b"] = 1;
x.b; //returns 1

for (p in x) document.write(p+";"); //writes "a;b;"

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");
}

如果你试图沙盒javascript代码，并禁用所有可能的方法来求值字符串到javascript代码中，要注意阻塞所有明显的eval/document。Function/setTimeout/setInterval/innerHTML和其他DOM操作是不够的。

给定任何对象o, o.constructor.constructor("alert('hi')")()将弹出一个警告对话框，其中包含单词"hi"。

可以写成

var Z="constructor";
Z[Z][Z]("alert('hi')")();

有趣的东西。

有些人会说这是品味问题，但是:

aWizz = wizz || "default";
// same as: if (wizz) { aWizz = wizz; } else { aWizz = "default"; }

三元操作符可以被链接到Scheme的(cond…):

(cond (predicate  (action  ...))
      (predicate2 (action2 ...))
      (#t         default ))

可以写成……

predicate  ? action( ... ) :
predicate2 ? action2( ... ) :
             default;

这是非常“实用的”，因为它可以在没有副作用的情况下对代码进行分支。所以不要:

if (predicate) {
  foo = "one";
} else if (predicate2) {
  foo = "two";
} else {
  foo = "default";
}

你可以这样写:

foo = predicate  ? "one" :
      predicate2 ? "two" :
                   "default";

也适用于递归:)

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

JavaScript没有块作用域(但它有闭包，所以让我们称它为偶数?)

var x = 1;
{
   var x = 2;
}
alert(x); // outputs 2