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Let's understand const in JavaScript

Let's understand const in JavaScript

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Rafi kadir
·

1 min read

ES2015 (ES6) introduced the const keyword to define a new variable. The value of a constant (const) can't be changed through reassignment

  • Variables defined with const cannot be Redeclared.
  • Variables defined with const cannot be Reassigned.
  • Variables defined with const have Block Scope.

The const variable cannot be reassigned.

Incorrect:

const x = 12;
    x = 13;
    x += 1;

// Uncaught TypeError: Assignment to constant variable.

Variables defined with const cannot be Redeclared.

const x;  
x = 5; //  Can't Do this

// Uncaught SyntaxError: Missing initializer in const declaration

Variables defined with const have Block Scope.

const a = 2; // You can use the same name out of Block

{
    const a = 3; // You can use same name in Block
    console.log(a); 
}

console.log(a);

OUTPUT:

3 2

  • There is no error

Const Array:

// You can create a constant array:
const name = ["a", "b", "c"];
// You can change an element:
cars[0] = "d";
// You can add an element:
cars.push("e");

But you can’t reassign the array

name = ["d","e","f"]
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