Javascript Encapsulation example

Question

Javascript Encapsulation example

Could someone help me with this function query:

var MyObject3 = function (a, b) {
   var obj = { myA : a, myB : b } ;
   obj.foo = function () { return obj.myA + obj.myB ; } ;
   obj.bar = function (c) { return obj.myA + c ; } ;
   return obj ;
} ;

I understand that obj.foo and obj.bar are closures. I started by executing:

 obj3 = MyObject3(1, 2) ;

The outcome was: {"myA" :1,"myB" :2}, which is expected. What confuses me is the following: if I change the value of obj3.myA to 4 with; > obj3.myA = 4 ; obj3 ; the result becomes: {"myA" :4,"myB" :2}. However, when I try > obj3.foo() ;, it returns 6. Shouldn't obj3.foo() be a closure resulting in 3 instead of 6?

javascript

Answer 1

Answer №1

The Function MyObject3 creates a new object within its scope:

var obj = { myA : a, myB : b } ;

Any reference to obj inside this function refers to the same object. This object is then returned by the function and stored in the variable obj3. Both obj within the MyObject3 scope and obj3 in the global scope point to the identical object.

In JavaScript, primitives such as numbers, booleans, and strings are passed by value, while objects are passed by reference. This means that:

var val1 = 1;
var val2 = val1;
val1 = 4;
console.log(val2); // will output 1

// however:

var obj1 = {foo: 'bar'};
var obj2 = obj1;
obj1.foo = 'baz';
console.log(obj2.foo); // will output 'baz'

Answer 2

The Function MyObject3 creates a new object within its scope:

var obj = { myA : a, myB : b } ;

Any reference to obj inside this function refers to the same object. This object is then returned by the function and stored in the variable obj3. Both obj within the MyObject3 scope and obj3 in the global scope point to the identical object.

In JavaScript, primitives such as numbers, booleans, and strings are passed by value, while objects are passed by reference. This means that:

var val1 = 1;
var val2 = val1;
val1 = 4;
console.log(val2); // will output 1

// however:

var obj1 = {foo: 'bar'};
var obj2 = obj1;
obj1.foo = 'baz';
console.log(obj2.foo); // will output 'baz'

Javascript Encapsulation example

Answer №1

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