在将变量声明为函数Object的新实例时，为什么IE6会出现“期望函数”错误？

Question

Why does the parentheses have to follow immediately after the new Function? The MSDN website was unclear regarding why this is an error.

// Fails but only in IE6
var greetings = new SayHello;
greetings();

// This works in IE6
var salutations = new SayHello();

function SayHello() {
 alert("Hello");
};

Answer 1

I don't think that code does what you think it does. Try it this way:

var greetings = new SayHello;
alert('calling the constructor');
greetings();

function SayHello() {
 alert("Hello");
};

You will see the "Hello" alert first then the "calling the constructor" alert, which I think is the opposite of what you expect. The new operator is calling the constructor and generating the alert. The greetings() line actually throws a type error since at that point greetings is just an object (an instance of SayHello). I'm guessing (since I don't have a copy) that IE6 just isn't calling the constructor when the parenthesis are missing so it seems broken in a different way.