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。

微软给JavaScript的礼物:AJAX

AJAXCall('http://www.abcd.com/')

function AJAXCall(url) {
 var client = new XMLHttpRequest();
 client.onreadystatechange = handlerFunc;
 client.open("GET", url);
 client.send();
}

function handlerFunc() {
 if(this.readyState == 4 && this.status == 200) {
 if(this.responseXML != null)
   document.write(this.responseXML)
 }
}

我可以引用道格拉斯·克罗克福德这本好书的大部分内容 JavaScript:好的部分。

但我只给你一个，总是使用===和!==而不是==和!=

alert('' == '0'); //false
alert(0 == ''); // true
alert(0 =='0'); // true

==是不可传递的。如果你使用===，它会给出false for 所有这些陈述都符合预期。

正如Marius已经指出的，可以在函数中使用公共静态变量。

我通常使用它们来创建只执行一次的函数，或者缓存一些复杂的计算结果。

下面是我以前的“单例”方法的例子:

var singleton = function(){ 

  if (typeof arguments.callee.__instance__ == 'undefined') { 

    arguments.callee.__instance__ = new function(){

      //this creates a random private variable.
      //this could be a complicated calculation or DOM traversing that takes long
      //or anything that needs to be "cached"
      var rnd = Math.random();

      //just a "public" function showing the private variable value
      this.smth = function(){ alert('it is an object with a rand num=' + rnd); };

   };

  }

  return arguments.callee.__instance__;

};


var a = new singleton;
var b = new singleton;

a.smth(); 
b.smth();

如您所见，在这两种情况下构造函数都只运行一次。

For example, I used this approach back in 2004 when I had to create a modal dialog box with a gray background that covered the whole page (something like Lightbox). Internet Explorer 5.5 and 6 have the highest stacking context for <select> or <iframe> elements due to their "windowed" nature; so if the page contained select elements, the only way to cover them was to create an iframe and position it "on top" of the page. So the whole script was quite complex and a little bit slow (it used filter: expressions to set opacity for the covering iframe). The "shim" script had only one ".show()" method, which created the shim only once and cached it in the static variable :)

访问:

http://images.google.com/images?q=disco

将以下JavaScript代码粘贴到浏览器的地址栏:

http://amix.dk/upload/awt/spin.txt http://amix.dk/upload/awt/disco.txt

享受JavaScript的迪斯科表演:-p

数字也是对象。所以你可以做一些很酷的事情，比如:

// convert to base 2
(5).toString(2) // returns "101"

// provide built in iteration
Number.prototype.times = function(funct){
  if(typeof funct === 'function') {
    for(var i = 0;i < Math.floor(this);i++) {
      funct(i);
    }
  }
  return this;
}


(5).times(function(i){
  string += i+" ";
});
// string now equals "0 1 2 3 4 "

var x = 1000;

x.times(function(i){
  document.body.innerHTML += '<p>paragraph #'+i+'</p>';
});
// adds 1000 parapraphs to the document