Const is not meant to make your element immutable! it only ensures that your element stays the same so you cannot assign to it a different element!

You can freeze the array with Object.freeze. This would make it so the elements cannot be changed.

const arr = [1, 2, 3];

arr.push(4); // arr = [1, 2, 3, 4]

const frozenArr = Object.freeze(arr);     

frozenArr.push(5); // Error: Cannot add property
frozenArr.pop(); // Error: Cannot delete property

Previous answer as it was, for reference

A const array only prevents further assignments but you are allowed to change the contents of it.

The best practice for immutable arrays is to make copies, i.e. use Array.slice() with no arguments or Array.from().

Example:

const originalArray = [1, 2, 3];

let firstNewArray = Array.from(originalArray);
firstNewArray.push(4);

let secondNewArray = originalArray.slice();
secondNewArray.push(5);

console.log(originalArray); // Output -> [1, 2, 3]
console.log(firstNewArray); // Output -> [1, 2, 3, 4]
console.log(secondNewArray); // Output -> [1, 2, 3, 5]

originalArray.push(9); // This is allowed
console.log(originalArray); // Output -> [1, 2, 3, 9]

originalArray = []; // Error: Assignment to constant variable

An array, number, string are all objects. They differ in the way they store values. A String are charcaters and therefore fixed if it has been declared const. An array is a construct of how multiple values are stored. This means that const sets the type imutable but not the values.