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{...}. . (constructor functions) "new".

.
"new" . :

          function User(name) {
this.name = name;
this.isAdmin = false;
}
let user = new User("Jack");
alert(user.name); // Jack
alert(user.isAdmin); // false
        

new :

this.
. this .
this. new User(...) :

          function User(name) {
// this = {}; (implicitly)
// this   
this.name = name;
this.isAdmin = false;
// this; (implicitly) 
}
        

let user = new User("Jack") :

          let user = {
name: "Jack",

isAdmin: false
};
        

new User("Ann") new User("Alice") . . . . new . new.

`new function() { }`

          let user = new function() {
this.name = "John";
this.isAdmin = false;
// ...   
//      
//   ..
};
        

. .

: `new.target`

: . new new.target. new:

          Inside a function, we can check whether it was called with `new` or without it, using a special `new.target` property.

It is undefined for regular calls and equals the function if called with `new`:

```js run
function User() {
alert(new.target);
}
// "new" :
User(); // undefined
//  "new":
new User(); // function User { ... }
        

new . new - - :

          function User(name) {
if (!new.target) { // new    
return new User(name); // new ...
}
this.name = name;
}
let john = User("John"); // new User   
alert(john.name); // John
        

new . new . new .

return. this . return :

return this.
return . return this. return this:

          function BigUser() {
this.name = "John";
return { name: "Godzilla" }; // <--   
}
alert( new BigUser().name ); // Godzilla,   
        

return ( ):

          function SmallUser() {
this.name = "John";
return; //  this 
}
alert( new SmallUser().name ); // John
        

return. .

new :

          let user = new User; // <--   
//  
let user = new User();
        

. this . new User(name) name sayHi:

          function User(name) {
this.name = name;
this.sayHi = function() {
alert( "My name is: " + this.name );
};
}
let john = new User("John");
john.sayHi(); // My name is: John
/*
john = {
name: "John",
sayHi: function() { ... }
}
*/
        

.
new . this .
.
JavaScript () : Date Set .

. . .

: 2 A B new A()==new B()

          function A() { ... }
function B() { ... }
let a = new A;
let b = new B;
alert( a == b ); // true
        

. . new this. obj:

          let obj = {};
function A() { return obj; }
function B() { return obj; }

alert( new A() == new B() ); // true
        

: 5 Calculator :

read() .
sum() .
mul() . :

          let calculator = new Calculator();
calculator.read();
alert( "Sum=" + calculator.sum() );
alert( "Mul=" + calculator.mul() );
        

          function Calculator() {
this.read = function() {
this.a = +prompt('a?', 0);
this.b = +prompt('b?', 0);
};
this.sum = function() {
return this.a + this.b;
};
this.mul = function() {
return this.a * this.b;
};
}
let calculator = new Calculator();
calculator.read();
alert( "Sum=" + calculator.sum() );
alert( "Mul=" + calculator.mul() );
        

: 5 Accumulator(startingValue) :

value. startingValue .
read() prompt value. value startingValue. :

          let accumulator = new Accumulator(1); //   1
accumulator.read(); //     
accumulator.read(); //     
alert(accumulator.value); //   
        

          function Accumulator(startingValue) {
this.value = startingValue;
this.read = function() {
this.value += +prompt('How much to add', 0);
};
}
let accumulator = new Accumulator(1);
accumulator.read();
accumulator.read();
alert(accumulator.value);
        

-- Constructor, operator new The JavaScript Language

Two functions one object

Is it possible to create functions A and B such as new A()==new B()?

          function A() { ... }
function B() { ... }

let a = new A;
let b = new B;

alert( a == b ); // true
        

If it is, then provide an example of their code.

Yes, its possible.

If a function returns an object then new returns it instead of this.

So they can, for instance, return the same externally defined object obj:

let obj = {};

function A() { return obj; }
function B() { return obj; }

alert( new A() == new B() ); // true

Create new Calculator

Create a constructor function Calculator that creates objects with 3 methods:

read() asks for two values using prompt and remembers them in object properties.
sum() returns the sum of these properties.
mul() returns the multiplication product of these properties.

For instance:

          let calculator = new Calculator();
calculator.read();

alert( "Sum=" + calculator.sum() );
alert( "Mul=" + calculator.mul() );
        

sandbox .

function Calculator() {

  this.read = function() {
    this.a = +prompt('a?', 0);
    this.b = +prompt('b?', 0);
  };

  this.sum = function() {
    return this.a + this.b;
  };

  this.mul = function() {
    return this.a * this.b;
  };
}

let calculator = new Calculator();
calculator.read();

alert( "Sum=" + calculator.sum() );
alert( "Mul=" + calculator.mul() );

sandbox.

Create new Accumulator

Create a constructor function Accumulator(startingValue).

Object that it creates should:

Store the current value in the property value. The starting value is set to the argument of the constructor startingValue.
The read() method should use prompt to read a new number and add it to value.

In other words, the value property is the sum of all user-entered values with the initial value startingValue.

Heres the demo of the code:

          let accumulator = new Accumulator(1); // initial value 1

accumulator.read(); // adds the user-entered value
accumulator.read(); // adds the user-entered value

alert(accumulator.value); // shows the sum of these values