Q:

can this example be considered as multiple inheritance in javascript..?

I heard that multiple inheritance is not supported in JavaScript.
Does the below example can be considered as Multiple Inheritance if no then can anyone please explain why...?
function A () {
  this.a = 'a'
};

function B () {
  this.b = 'b'
};

function AB () {
  A.call(this);
  B.call(this);
};

var obj = new AB();
console.dir(obj);
//Output: {a: "a", b: "b"}

A:

Can the below example be considered Multiple Inheritance?

No

Can anyone please explain why?

Your AB (which I will call C from here on out) function doesn't actually extend A nor does it extend B:

function A () {
  this.a = 'a';
}

function B () {
  this.b = 'b';
}

function C () {
  A.call(this);
  B.call(this);
}

a = new A();
console.log('a is A', a instanceof A);

b = new B();
console.log('b is B', b instanceof B);

c = new C();
console.log('c is A', c instanceof A, 'c is B', c instanceof B);

You don't have any inheritance at all in that example. You do have function composition.
If you wanted to have inheritance, the C function would need to have a prototype that points to an instance of either A or B:

function A () {
  this.a = 'a';
}

function B () {
  this.b = 'b';
}

function C () {
  A.call(this);
  B.call(this);
}

C.prototype = new A();
//or
//C.prototype = new B();

a = new A();
console.log('a is A', a instanceof A);

b = new B();
console.log('b is B', b instanceof B);

c = new C();
console.log('c is A', c instanceof A, 'c is B', c instanceof B);

Note that because the C function has a single prototype you can only have single inheritance.

For object composition, it would be common to see a pattern along the lines of:

function A () {
  this.a = 'a';
}

function B () {
  this.b = 'b';
}

function C () {
  this.a = new A();
  this.b = new B();
}

a = new A();
console.log('a is A', a instanceof A);

b = new B();
console.log('b is B', b instanceof B);

c = new C();
console.log('c.a is A', c.a instanceof A, 'c.b is B', c.b instanceof B);

