你认为每个程序员都应该知道JavaScript的哪些“隐藏特性”?

在看到以下问题的优质答案后,我认为是时候向JavaScript请求它了。

HTML的隐藏特性 CSS的隐藏特性 PHP的隐藏特性 ASP的隐藏特性。网 c#的隐藏特性 Java的隐藏特性 Python的隐藏特性

尽管JavaScript可以说是目前最重要的客户端语言(问问谷歌就知道了),但令人惊讶的是,大多数web开发人员很少意识到它的强大。


当前回答

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 :)

其他回答

==运算符有一个非常特殊的属性,它创建了这个令人不安的等式(是的,我知道在其他动态语言中,如Perl,这种行为是预期的,但JavaScript通常不会尝试在比较中聪明):

>>> 1 == true
true
>>> 0 == false
true
>>> 2 == true
false

语法糖:内联for循环闭包

var i;

for (i = 0; i < 10; i++) (function ()
{
    // do something with i
}());

几乎打破了Douglas Crockford的所有代码惯例,但我认为它看起来很漂亮,从未减少:)


选择:

var i;

for (i = 0; i < 10; i++) (function (j)
{
    // do something with j
}(i));

您可以根据异常的类型捕获异常。引自MDC:

try {
   myroutine(); // may throw three exceptions
} catch (e if e instanceof TypeError) {
   // statements to handle TypeError exceptions
} catch (e if e instanceof RangeError) {
   // statements to handle RangeError exceptions
} catch (e if e instanceof EvalError) {
   // statements to handle EvalError exceptions
} catch (e) {
   // statements to handle any unspecified exceptions
   logMyErrors(e); // pass exception object to error handler
}

注意:条件捕获子句是Netscape(因此也是Mozilla/Firefox)扩展,它不是ECMAScript规范的一部分,因此不能依赖于特定的浏览器。

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);
}

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