Const Block Scope

An array declared with const follows block scope rules.

Therefore, an array declared within a block behaves differently from one declared outside the block.

Example

const cars = [“Saab”, “Volvo”, “BMW”];
// Here cars[0] is “Saab”
{
const cars = [“Toyota”, “Volvo”, “BMW”];
// Here cars[0] is “Toyota”
}
// Here cars[0] is “Saab”

An array declared with ‘var‘ does not adhere to block scope rules.

Example

var cars = [“Saab”, “Volvo”, “BMW”];
// Here cars[0] is “Saab”
{
var cars = [“Toyota”, “Volvo”, “BMW”];
// Here cars[0] is “Toyota”
}
// Here cars[0] is “Toyota”

Redeclaring Arrays

You can redeclare an array that was initially declared with ‘var‘ anywhere in a program.

Example

var cars = [“Volvo”, “BMW”]; // Allowed
var cars = [“Toyota”, “BMW”]; // Allowed
cars = [“Volvo”, “Saab”]; // Allowed

It’s not permitted to redeclare or reassign an array to a constant (const) in the same scope or block.

Example

var cars = [“Volvo”, “BMW”];     // Allowed
const cars = [“Volvo”, “BMW”];   // Not allowed
{
  var cars = [“Volvo”, “BMW”];   // Allowed
  const cars = [“Volvo”, “BMW”]; // Not allowed
}

It’s not allowed to redeclare or reassign an existing constant array (const) in the same scope or block.

Example

const cars = [“Volvo”, “BMW”];   // Allowed
const cars = [“Volvo”, “BMW”];   // Not allowed
var cars = [“Volvo”, “BMW”];    // Not allowed
cars = [“Volvo”, “BMW”];         // Not allowed

{
  const cars = [“Volvo”, “BMW”]; // Allowed
  const cars = [“Volvo”, “BMW”]; // Not allowed
  var cars = [“Volvo”, “BMW”];   // Not allowed
  cars = [“Volvo”, “BMW”];       // Not allowed
}

Redeclaring an array with ‘const‘ in another scope or block is allowed.

Example

const cars = [“Volvo”, “BMW”];   // Allowed
{
  const cars = [“Volvo”, “BMW”]; // Allowed
}
{
  const cars = [“Volvo”, “BMW”]; // Allowed
}