Question

While writing javascript, one can define a method in 3 different ways.

1] A function in global namespace

function doSomething();

2] A function that is member of a function

function Clazz() {}
Clazz.doSomething = function(){};

3] A function that is memeber of the instance of function

function Clazz() {}
Clazz.prototype.doSomething = function(){};

Depending upon the code organization, one can choose one of the above methods over others.

But purely from performance standpoint which is the most efficient one? (especially between 1 and 2)

Will your answer be different if doSomething has arguments?

Answer 1

From a pure performance POV, 1 should be the fastest. The reason being that it would require less work to setup the scope chain & execution context. Also if you access any global variables from within the function, the resolution will be fastest with 1, again simply because of the depth of scope chain.
As a general rule further up (near to the global) an object is in the scope, the faster it is. for the same reason accessing property a.b will be faster than accessing a.b.c

The performance gain might not be too much in case of a simple function call, however it can mount up if say you call the function n a loop.