Question

Is there any difference between the below declarations?

declaration 1:

someName.test1 = function() {alert("test1")}

declaration 2:

someName.protoype.test2 = function() {alert("test2")}

Duplicate of Difference Between Class Properties and Function Prototype in Javascript

Answer 1

Yes, there’s a difference:

someName.test1 = function() {alert("test1")} 

adds this function to the object (or class) someName.

someName.protoype.test2 = function() {alert("test2")}

adds this function to all instances of class someName

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For a real example, look at this:

Object.getOwnPropertyNames = function(obj)  { ... };

which is just a function namespaced into the Object class, taking the object of interest as its first parameter, whereas if it had been written:

Object.prototype.getOwnPropertyNames = function() { ... };

Then every Object would have that method and it would be used like this:

obj.getOwnPropertyNames();

[but don’t do that, since adding methods to the Object prototype is frowned upon!]