Interview-Based Concept (CONST)

Concept of const is a little bit tricky which you should understand if you are a javascript developer. When anybody didn't want to override the code then we use const in JS, Let's understand with an example.

const a=10;

a=11; // I can't change that 

I can't again re-assign the value, it doesn't mean that I can't put the value inside it. for example, I have an object

const x={b:12, c:13, d:14};

In this object, we can easily change the inside values, update the values and insert the values as well. But we can't reassign with the same name.

x.b=22; // Its a valid statement

x.c=23; // Its a valid statement

x.e=22; // Its a valid statement

x.f=21; // Its a valid statement

All the above statements are valid and work without an error. I am updating and assigning new values in the object. But we can't do reassign it like this

var x=10; // Not Valid

let x=[]; // Not Valid

const x={} // Not Valid

These 3 above statements are not valid because we already declared the object with const which name is "x".

In the same case of an array, we can modify the array inside elements, push the elements, pop or delete element as well.

const momi=["first","second","third"];

momi.push('forth'); //vaid statement

Output: ["first", "second", "third", "forth"];

momi.pop(); //valid statement 

Output: ["first", "second", "third"];

When you're adding to an array or object you're not re-assigning or re-declaring the constant, it's already declared and assigned, you're just adding to the "list" that the constant points to

const just means the variable cannot be reassigned, not that you can't manipulate it.

Let see const declaration with a function, whats happen

const f=()=>{ } //Arrow function with name 'f'

var f={Hello}; //Not valid

f=30; //Not valid

const f=()=>{ } // Not valid

let f=()=>{ } //Not Valid

Here 'f' is pointing to a specific function we cant reassign.

Keep it in your mind, Javascript supports overriding, not overloading. 

?

Regards: Azeem Aleem