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In javascript how does the below code works

In Javascript how does the below code works.

var a = {
prop1: "a",
prop2: "b",
fun: function() {
return this.prop1 + " " + this.prop2;
}

}
var a2 = a;
a.fn = "v";
a = {};
if (a === a2) {
console.log(true);
} else {
console.log(false);
}

The above code prints false.

But if I comment out the line a={} the value which prints on console is true.

var a = {
prop1: "a",
prop2: "b",
fun: function() {
return this.prop1 + " " + this.prop2;
}

}
var a2 = a;
a.fn = "v";
//a={};
if (a === a2) {
console.log(true);
} else {
console.log(false);
}

How the above code works, as Both variables(a and a2) points to the same object but when I initialized a with {} it gave false.

a

{}

a2

a

{}

var a2=a;

4 Answers
4

...as Both variables(a and a2) points to the same object ...

They don't anymore, as of this line:

a={};


At that point, a2 refers to the old object, and a refers to a new, different object.

a2

a

a2 = a doesn't create any kind of ongoing link between the variable a2 and the variable a.

a2 = a

a2

a

Let's throw some Unicode-art at it:

After this code runs:

var a = {
prop1: "a",
prop2: "b",
fun: function() {
return this.prop1 + " " + this.prop2;
}

}
var a2 = a;
a.fn = "v";


At this point, you have something like this in memory (with various details omitted):

Those "Ref" values are object references. (We never actually see their values, those values are just made up nonsense.) Notice that the value in a and the value in a2 is the same, however.

a

a2

If you do a === a2 at this point, it will be true: Both variables refer to the same object.

a === a2

true

But when you do this:

a={};


At this point, a === a2 is false: The variables refer different objects.

a === a2

false

In first case after this line var a2 = a; a is again initialized as an empty object, so now a & a2 are two different reference

var a2 = a;

a

var a = {
prop1: "a",
prop2: "b",
fun: function() {
return this.prop1 + " " + this.prop2;
}

}
var a2 = a;
a = {};
console.log(a, a2)
if (a === a2) {
console.log(true);
} else {
console.log(false);
}

In second case they point to same location, so adding a new property will reflect in the other too.

var a = {
prop1: "a",
prop2: "b",
fun: function() {
return this.prop1 + " " + this.prop2;
}

}
var a2 = a;
a.fn = "v";
console.log(a, a2)
//a={};
if (a === a2) {
console.log(true);
} else {
console.log(false);
}

In the first case :

var a2 = a; // now a2 and a have reference (or point to) the same object"
a= {}; // a now points to new reference


Since both a and a2 points has different references i.e why it returns false in first.

When you comment a= {} both a and a2 points to same location or stores same reference that is why it returns true.

a= {}

a2

a

a2

a

a={};

a2

var a = {
prop1: "a",
prop2: "b",
fun: function() {
return this.prop1 + " " + this.prop2;
}

}
var a2 = a;
a.fn = "v";
a = {};
console.log(a);
console.log(a2);
if (a === a2) {
console.log(true);
} else {
console.log(false);
}

Look at your code carefully. a is not innitialized to {}. It was initialized in the first line where it says var a =. I have printed out both values for you. var a2 gets the value of var a, not the reference so when var a changes, var a2 does not change.

{}

var a =

var a2

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