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Static method instead of Prototype method Javascript

When instance function are called in a class each instance of object get own copy of function but in prototype method and static method no copy is created , they belong to class, so if they both doesn't create a copy of their function, so why do we have static function if we can simply use prototype method if we don't want to copy??
I am a little bit confuse, if anyone can explain it will be a great help

In order to use a prototype/instance method, you need to either have an instance of an object or specifically access the type's .prototype. For methods that don't require an instance, a static method provides simpler syntax. Think of the String.fromCharCode() method as an example. It wouldn't make sense to say:
let str = "dummy string".fromCharCode(127);
The extra string instance there is just a distraction from what you're really trying to do:
let str = String.fromCharCode(127);
This applies good programming practices of reduced coupling (not requiring an instance in order to invoke a method that doesn't need it) and information hiding (by not exposing a method on instances of objects which doesn't pertain to those specific objects).

A static method does not exist on instances. Prototype methods do. So, if you want to call someArr.filter(x => x > 5) that would be an instance method that works on the given array.
An example of astatic method is Array.isArray(someArr). It makes very little sense to make the static method an instance method because you'd need an instance before calling it. That would lead to code like someArr.isArray(someArr) which is illogical - you need an array to check if something is an array. And that can very easily be fail spectacularly if someArr is not in fact an array:
const someArr = {
isArray() { return true; },
filter() { return "I am not an array"; },
};
console.log(someArr.isArray(someArr));
console.log(someArr.filter(x => x > 5));
Yes, that example is indeed highly illogical in order to highlight why it is weird. Assuming .isArray() was an instance method, you could create a new array in order to use it to call [].isArray(someArr). But that method does not require any instance data. The object created exists only to give you access to the method and is discarded immediately afterwards. That design is still not sensible.

Both static methods and prototype methods exist independent from any instances. The difference is that a prototype method expects to be called on an instance, i.e. to have an instance passed as the this argument, whereas the static method does not require an instance and expects none.
Even without placing them anywhere on the class, we can see this distinction in the following example:
function myStaticMethod(arg) {
console.log('Doing something with '+arg);
}
function myMethod(arg) {
console.log('Doing something with '+this+' and '+arg);
}
const myInstance = new MyClass();
myStaticMethod('value');
myMethod.call(myInstance, 'value');
Now the .call() syntax is not very ergonomic, we prefer myInstance.myMethod('value'), so that is why we place the method on the prototype object of the class, having it inherited by all instances.
For static methods, this is not necessary. They don't need an instance, we don't want to call them on an instance, we want to call them as MyClass.myStaticMethod('value') so that is where we place them. We could put them on the prototype as well, but that would lead to confusion (myInstance.myStaticMethod()), name collisions, and unncessarily long invocations (MyClass.prototype.myStaticMethod()). It's imaginable to write new MyClass().myStaticMethod(), but there you would unnecessarily create an instance that is not required (and it might not even be possible to create).

Make a javascript "function object" inherit from another

In Javascript, it's possible to have some kind of inheritance, by using function contructors and their "prototype" attribute (i.e the "parent of future instances"), or more recently Object.create(), to get new objects.
However recently I needed to "override" the Jquery object ("$") for one of my projects, that is to say, provide a similar function, which also has all the fn/extend/... [inherited] attributes of the original "jQuery" factory function.
The goal was to have a "$()" function which always received "window.parent" as the second parameter by default, so that the whole program modified the parent frame and not the iframe in which the program was loaded.
Typically I expected to be able to do something like this:
var oldJQ = $;
$ = function (selector) {
return oldJQ(selector, window.parent);
}
$.__proto__ = oldJQ .__proto__;
$.extend({...}); // must work
Despite numerous attempts, I couldn't get it to work, I always got simple objects instead of real functions when using the "new" keyword, or the inheritance didn't work. I found alternative ways (for example, by copy-pasting all attributes from $ into my new function object), but it seems to me like a horrible way of doing stuffs.
Is there any way to have a new function object which has, as a parent/prototype, the original $ object ?

While functions are objects in javascript, they aren't regular objects. Specifically, they're objects for which inheritance is broken. Functions are not the only such objects in the language, DOM elements are similarly handicapped. That's one reason jQuery is implemented as wrapper around DOM rather than extending the DOM's features via inheritance.
Fortunately, while OOP doesn't work in this case, we can take inspiration from jQuery itself and use FP to do what we need. In other words, while you can't inherit functions, you can wrap it in another function.
For example, if you need a special console.log function for your app that sends logs back to your server you can override it by redefining it:
var log_orig = console.log;
console.log = function () {
ajaxlog([].slice.call(arguments,0).map(function(x){
return JSON.parse(x);
}).join(',');
log_orig.apply(console,arguments);
}
Or if you want a special version of $ that does something extra:
function $$ () {
/*
* do extra stuff
*/
return $.apply(null,arguments);
}
Or if you want to override $ instead if wrapping:
var old$ = $;
function $ () {
/*
* do extra stuff
*/
return old$.apply(null,arguments);
}

Mixing datatypes, functions and objects

When you use require and loads a module, you seems capable of create a function with properties or a object that can be invoked as a function.
console.log(require('events').EventEmitter);
//{ [Function: EventEmitter] defaultMaxListeners: 10, listenerCount: [Function] }
I have done this before* using the require module so I can replicate it. But I want to create more manually. I have some questions in this regards:
Is possible replicate this manually, harcoded without require?
Is possible to create any type of property like getters or setters?
Is posible to create one of these 'objects' when you use a constructor?
Thanks in advance.
*Or I remember that, I have a terrible memory
Edited:
To be clear: I'm not talking about prototype. In my example you can see that, for example, defaultMaxListeners dont come from prototype. In code:
EventEmitter.defaultMaxListeners // 10
EventEmitter.prototype.defaultMaxListeners // undefined
EventEmitter() //No error

Is possible replicate this manually, harcoded without require? Is
possible to create any type of property like getters or setters? Is
posible to create one of these 'objects' when you use a constructor?
Yes
In JS, functions are also objects. You can attach properties to them like any other object. Also, in JS, functions can be used as both functions as well as object constructors.
The following example shows what you can do to a function. I'm using Classical OOP terms, since I don't know what they call them in JS.
function SomeConstructor(){
this.instanceProperty = 'foo';
}
// Instance Method
SomeConstructor.prototype.method = function(){
console.log('method');
}
// Static Method
SomeConstructor.staticMethod = function(){
console.log('static');
}
var test = new SomeConstructor();
test.method();
SomeConstructor.staticMethod();

Is it acceptable to add an attribute to a JavaScript function?

Is it acceptable to add an attribute or value to a JavaScript function?
Example:
var f = 1;
function foo (param) {
f++;
}
var fooFunc = foo;
fooFunc.dummy = f;
console.log('fooFunc: ' + fooFunc);
console.log('fooFunc.dummy: ' + fooFunc.dummy);
The above example creates a function (foo), then assigns it to a new variable (fooFunc) and then adds a dummy attribute to fooFunc.
When run, this example prints the text of the function first, and then it prints the expected value (1 in this case). When printing the function, it doesn't show any indication of the dummy value:
fooFunc: function foo(param) {
f++;
}
fooFunc.dummy: 1
JsFiddle here - open the browser's JavaScript console to see the log messages: http://jsfiddle.net/nwinkler/BwvLf/
Why does this work? And where is the dummy attribute stored, and why isn't it printed when I log the function?
Lastly, even if this works, is it a good idea (or an acceptable practice) to use this? I don't want to start an open ended discussion on this, but rather see if there's documented uses of this, or people discouraging this in JavaScript coding guidelines.

Everything except primitives ( null, undefined, number, string, boolean ) in JavaScript are objects. So functions are basically objects.
Objects in JavaScript can have properties and methods, hence functions too.
all functions inherit from Function.prototype and has certain properties ( name, length ) and methods ( .call, .apply ) coming through this chain.
It is sometimes very useful to keep properties attached to the function itself, like cache information, number of invocations etc. There is nothing wrong out in using it this way.
More details : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function

Let's have a look at ECMAScript documentation (Which is the standard JavaScript is based on). Here's the 3rd. version of it:
http://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%203rd%20edition,%20December%201999.pdf
Go to chapter 15, Native ECMAScript Objects.
15.3 > Function objects.
There's a lot of interesting information there concerning your question, but the first thing worth noticing is that function is an object.
As an object, it has attributes (predefined and that you can assign yourself).
For example, try:
console.log('fooFunc.name: ' + fooFunc.name);
It should display "foo" in your case.
Since it's documented quite well, you can use it as a standard way, though it is not so well-spread and may seem a bit unusual.
Hope this helps.

It is normal object behavior, whether "acceptable" or not.
By using the function keyword you are actually calling the native predefined Function() constructor. Like any object constructor it returns an object after building it. Like any object, the returned object can have properties, including other functions as method properties.
var adder = function(a, b){return a+b};
adder.subtracter = function(a, b){return a-b};
console.log(adder(1,2)); // 3
console.log(adder.subtracter(1,2)); // -1
TIP: if you want to see the adder object and its subtracter method, switch to DOM view from Console view after running the above code in console and then search for "adder". You'll see the object there, and then you can collapse to see what it's made from, including a subtracter object.
Of course, a function object is a special native object, which makes it possible to make calls like this: adder() and actually run some code. The fact that a function object is harder to inspect for custom attached properties, combined with its native special object treats (read built-in restrictive behavior), should give you a hint that, while it's possible, attaching custom properties is not the intended nor a good use of a function object.

Javascript plugins design pattern like jQuery

Could someone write down a very simple basic example in javascript to conceptualize (and hopefully make me understand) how the jQuery plugin design pattern is done and how it works?
I'm not interested in how creating plugin for jQuery (so no jQuery code here at all).
I'm interested in a simple explanation (maybe with a bit of Javascript code) to explain how it is done the plugin concept.
Plz do not reply me to go and read jQuery code, I tried, but I it's too complex, otherwise I would have not post a question here.
Thanks!

jQuery has a library of functions stored in an internal object named fn. These are the ones that you can call on every jQuery object.
When you do $("div.someClass") you get a jQuery object containing all <div> elements of that class. Now you can do $("div.someClass").each( someFunction ) to apply someFunction to each of them. This means, that each() is one of the functions stored in fn (a built-in one in this case).
If you extend (add to) the internal fn object, then you automatically make available your custom function to the same syntax. Lets assume you have a function that logs all elements to the console, called log(). You could append this function to $.fn, and then use it as $("div.someClass").log().
Every function appended to the fn object will be called in such a way that inside the function body, the this keyword will point to the jQuery object you've used.
Common practice is to return this at the end of the custom function, so that method chaining does not break: $("div.someClass").log().each( someFunction ).
There are several ways to append functions to the $.fn object, some safer than others. A pretty safe one is to do:
jQuery.fn.extend({
foo: function() {
this.each( function() { console.log(this.tagName); } );
return this;
}
})

Tomalak already posted almost everything You need to know.
There is one last thing that helps jQuery do the trick with the this keyword.
it's amethod called apply()
var somefunction=function(){
alert(this.text);
}
var anObject={text:"hello"};
somefunction.apply(anObject);
//alert "hello" will happen
It really helps in creating abstractions so that framework/plugin users would just use this as intuition tells them, whatever there is inside Your code

It works, as many other js frameworks, using javascript prototype orientation.
For instance you can declare a simple function
var alertHelloWorld = function() {
alert('hello world');
}
And then tie it to an existing object (including DOM nodes)
document.doMyAlert = alertHelloWorld;
If you do this
document.doMyAlert();
The alertHelloWorld function will be executed
You can read more about javascript object prototyping here