无法理解ECMAScript规范中的短语

Question

I'm reading ECMAScript Language Specification and can't understand properly one phrase.

The phrase is

Every object created by a constructor has an implicit reference ( called the object's prototype ) to the value of its constructor's "prototype" property.

ECMAScript - 4.2.1 Objects - second paragraph

I can't uderstand the phrase in parenthesis called the object's prototype .

The phrase in parenthesis tell that a prototype is an implicit reference.

My question is : Prototype is reference? An implicit reference is an prototype? Actually? I always thought that the prototype is the object. But ECMA says that an implicit reference to the value of constructor's "prototype" property is object's prototype.

I correctly understand what the ECMAScript says, or my understanding is wrong?

Answer 1

I think we could simply reword it to

"Every object created by a constructor has an implicit reference to the value of its constructor's "prototype" property, called the object's prototype."

Answer 2

All objects in javascript get their properties and methods from its prototype. Prototype word refers to "a first or preliminary version of something". So, whenever you create anything (class or function) in javascript which can have its object created, its initial skeletal structure can be referred to as a prototype. So, suppose you defined a javascript class with a variable printStatement and a method print(), each object of that class will definitely contain these two things. How? from the prototype you created.

function Printer(statement) {
    this.printStatement = statement;
    this.print = function()
    {
      // Any send to printer logic
      // this.printStatement.sendToPrinter();
    }
} 

The above statement defines a prototype for Printer function.

You can call it as Printer("Print this line").print();

Now, some 50 lines later in your file, you think that this object should have one more function, ReadPrint statement. You can access the prototype through the object itself and add it in memory.

Printer.prototype.ReadPrint = function(){
      //whatever it does
}

and from the next lines, you can call it as Printer.ReadPrint()

Since in javascript, prototype is a open available object. You can add your own stuff to its very definition, like

String.prototype.findAllIndexesOf = function(){
     //whatever it does.
}

When you do that, .findAllIndexesOf() will be available on every string object in the following lines and can be called in the same way you would call split(), trim() and other methods on any string object.

Do understand that adding functions and properties through this way does not affect the original code, so, if you have to add functions to a prototype of different objects which are available in javascript, add those functions in one file, and you would have to include this file on your pages.

See the link below

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects

and check out the Built-in objects section. It shows available javascript objects and shows usage of prototype. Click on any object like Array or string, and you will understand the functioning of prototype.