为什么带有新函数的setTimeout会忽略等待间隔？

Question

When trying to do this:

setTimeout(function(){alert("Boo");}, 500);

I accidentally wrote this:

setTimeout(new function(){alert("Boo");}, 500);

The former version waits 500 millis, then alerts. The latter alerts immediately.

Why does adding new in front of the function cause this behavior?

Answer 1

使用new创建一个使用匿名函数作为其构造函数的新对象，因此您的函数会立即运行并发出警报。

Answer 2

后者实例化一个Object并立即调用其构造函数。

Answer 3

new function(){alert("Boo");} 

is an equivalent of

var temp1 = function(){alert("Boo");};
var temp2 = new temp1();

second line as you see invokes your function using temp1 as a constructor.