javascript - why is declared function invoked at runtime

Question

The mere declaration of a function to an object leads to its invocation

var a  = {};
a.xyz = new function() { 
    alert("dosomething");
}

I would expect, that the declared function a.xyz only gets invoked when I call it:

a.xyz();

What is wrong with my assumption?

Answer 1

Remove new and everything will be fine:

var a  = {};
a.xyz = function() { 
    alert("dosomething");
}

JSFiddle: http://jsfiddle.net/vnj8pzm1/

EDIT: More about IIFE - Immediately-Invoked Function Expression (IIFE)

Answer 2

When you put new in front of your function definition, your function is being called as a constructor immediately.

As iceless mentioned, you should not have new in front of your function defintion. However, what iceless mentioned in the comment is incorrect

new function() {} or new function() {}(); will invoke the function just like function() {}(); or (function() {}());

new function() {} will create a new instance of an anonymous type, so in your code a.xyz is an object

if you change it to just function(){}() it would execute the function immediately and return nothing. See http://jsfiddle.net/mendesjuan/kzhg9ggu/