why this way "this.foo = new (function () {..})();" vs. "this.foo = function (){...};"

Is there any differe开发者_如何转开发nce in the two definitions and assignments of functions?

this.foo = new (function () {..})();

vs.

this.foo = function (){...};

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In the first example, it's creating a function and executing it, assigning the result to this.foo. In the second example, it's creating the function and assigning the function itself to this.foo.

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The main difference is calling the function with a "new" and assigning the anonymous function to a variable

ECMA 262 15.3.2: When Function is called as part of a new expression, it is a constructor: it initialises the newly created object.

So this.foo = new (function () {..})(); creates a new object and assigns it to this.foo

and

this.foo = function (){...}; defines an anonymous function and assigns it to this.foo

also another way is this.foo = (function () {..})(); (without the "new") will call the function and assign its return value to this.foo

In your case if you alert:

var foo = new (function () {})();
var bar = function() {};
var baz = (function () {return "boo";})(); // without the "new"

alert(foo); // will alert [object Object], the newly created object
alert(bar); // will alert function) {}, the function itself
alert(baz); // will alert "boo", the functions return value

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Your first example is plain wrong, have you actually tried it? If you want to use new and the Function constructor it works like this:

foo = new Function("function body");

(This is the worst possible way of defining a function)

Example 2 is the way to go.