Javascript ES6 Const Keyword

Learn Javascript ES6 Const keyword

Published June 17, 2021

Const Keyword
Const Keyword Rules
Const Keyword Block Scope Example
Const cannot be Redeclared Example
Const must be Declared before use

Const Keyword

The const keyword was introduced in ES6. The const keyword allows you to declare a constant(an unchangeable value). const is similar to let, except that it’s value cannot be changed.

Const Keyword Rules

Constant defined with const have Block Scope.
Constant defined with const cannot be Redeclared.
Constant defined with const must be Declared before use.

Const Keyword Block Scope Example

const x = 20;
console.log("x outer scope value: "+x);

{
  const x = 10;  // Const x means value cannot be changed
  console.log("x inner Scope with let : "+x);
  
  //x =15; // if you try to update with new value it will raise error.
}

//x = 30;  // if you try to update with new value it will raise error.
console.log("x outer scope value: "+x);

Const cannot be Redeclared Example

const a = 20;

const a = True; //Generate the error

console.log(a);

Const must be Declared before use


x = 30;          // const must be Declared before use
console.log(x);  // variable without declaration considered as var