passing object in javascript

Question

I know objects are passed by reference in javascript. so when I'm mutating an object in some other functions then it should be reflected in the initial object, which is not a case here, I might be missing something, it would be great if someone could help. here in the modify function I'm changing the object obj1 but still, it is showing the initial object.

Code

  obj1 ={
      b:{
        c:'c'
      },
      d:{
        g:{
          k:'k'
        }
      }
    }

let modify = (obj1) => {
  obj1 = obj1.b ;
}

console.log(obj1);
modify(obj1);
console.log(obj1);

Output

//output of console1
        [object Object] {
      b: [object Object] {
        c: "c"
      },
      d: [object Object] {
        g: [object Object] { ... }
      }
    }

//output of console2
    [object Object] {
      b: [object Object] {
        c: "c"
      },
      d: [object Object] {
        g: [object Object] { ... }
  }
}

Tycho · Accepted Answer · 2021-01-10 18:58:48Z

1

What your code does is changing the reference on obj1 instead of changing something in the object that the reference if referring to.. Try replacing something in the object like the modified code below.

 obj1 ={
      b:{
        c:'c'
      },
      d:{
        g:{
          k:'k'
        }
      }
    }

let modify = (obj1) => {
  obj1.d = obj1.b ;
}

console.log(obj1);
modify(obj1);
console.log(obj1);

answered Jan 10, 2021 at 18:58

Tycho

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Comments

sonEtLumiere · Accepted Answer · 2021-01-10 18:56:30Z

0

You are not modifying your original object, you are just accessing his property:

let obj1 = {
a: 1,
b: 2
}

obj1 = obj1.b ;
console.log(obj1);

If you create an object from other object, you are passing the reference to his object, to see how the original object is mutated check out this example:

let obj1 = {
a: 1,
b: 2
}

console.log(obj1)
let obj2 = obj1;
obj2.c = 3;
console.log(obj1);

answered Jan 10, 2021 at 18:56

sonEtLumiere

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Comments

Ted Brownlow · Accepted Answer · 2021-01-10 18:46:48Z

0

obj1 = obj1.b doesn't mutate anything because it merely re-assigns obj1 within the scope of modify(). However, any change you make to obj1, such as obj1.b.c='not c' will mutate the original object.

Here's an example that hopefully demonstrates this.

obj1 = {b:2}
obj2 = obj1
obj1 = 2
console.log(obj2);

answered Jan 10, 2021 at 18:46

Ted Brownlow

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