As you have mentioned that calling the constructor without the “new” keyword is a common mistake and I believe in this case JSLint will help catch these kind of mistakes early.

Another thing that you might try, though I believe this is not a pretty technique, is:

if ( !(this instanceof Foo) ) { return new Foo(); }

This will ensure that if Foo() is called without the new operator, still it will return an instance of Foo.

Cheers!

I think two more points will complete the post:

1. What happens when a constructor function is called without the “new” operator (very simple and basic, but a common mistake):
e.g


function Foo() {
this.name = 'Foo' ;
}

var f = Foo(); // => we are not using "new"
alert(window.name) // => 'Foo'


2. The “Constructor Pattern” or neo-classical constructors by Douglas Crockford

function Foo(param) {
var instance = {}; // empty object
// private members
var privateField_name = param; // => private field
//public member
instance.name = privateField_name;
return instance;
}

//usage
var a = Foo("Wallaby");
alert(a.name); // => 'Wallaby'


In this pattern we neither use “new” operator nor “this”.

Thanks
HIrak–

Now we can define our styles for the target browsers in the following manner

#test.safari div {margin: 0; padding: 0} etc. etc.

The advantage is, this lets you use same stylesheet for all browser and also apply small hacks and handle the small 1% edge cases. Just a thought, let me know what you think about this.

Thanks for passing this on.

http://www.nczonline.net/blog/2010/01/05/interviewing-the-front-end-engineer/
http://www.nczonline.net/blog/2007/03/27/surviving-an-interview-with-me/

may be you might have read them in the past.

Thanks,
Amit