Javascript：给setTimeout的函数调用是什么？ [英] Javascript: What does the function given to setTimeout get called with?

问题描述

我有这样的代码：

  setTimeout（foo，600）; 
  

我一直认为 foo 任何参数，例如：

  function foo（）{/ * bars * /} 
 
  
 function foo（a）{alert（a）; / * bars * /} 
  
弹出显示-7的警报。这个数字代表什么？
解决方案
这是它计划运行它的时间差（以毫秒为单位） 
  alert（setTimeout（function（a）{alert（a）}，2000） 
  
如果您及时清除第一个警报，您将看到下一个警报是-10到10如果你等待几秒钟，你会看到在等待减去2000的时间周围的东西。
 
 
 
 setInterval也可以看到同样的事情。在Firebug中运行以下命令：
  setInterval（function（a）{alert（a）;}，2000）; 
  
尝试快速关闭警报，它将再次为0。 
 注意这是在Firefox Mac上，其中保持警报打开将停止处理Javascript，所以定时器不会执行，直到我关闭警报。上述测试的行为在其他浏览器
 
中可能会有所不同
I have code like this:
setTimeout(foo, 600);
I always thought that foo didn't take any arguments, e.g.:
function foo() { /* bars */ }
However, doing the following:
function foo(a) { alert(a); /* bars */ }
Popped up an alert displaying -7. What does this number represent?
解决方案
It is the time difference (in milliseconds) from when it was scheduled to run it and when it actually ran.
alert(setTimeout(function(a) { alert(a) }, 2000));
If you clear the first alert in time, you will see the next alert is somewhere -10 to 10.  If you wait a few seconds, you will see something that is around the time you waited minus 2000.

The same thing can be seen for setInterval.  Run the following in Firebug:
setInterval(function(a) { alert(a); }, 2000);
Try closing the alert quick, it will be around 0 again.  Leave it open - it will give you a large value.

Note This is on Firefox Mac, where keeping an alert open will halt processing of Javascript, so the timer does not execute until I close the alert.  The behavior of the tests above may be different in other browsers

                        
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