Why can't I do array[-1] in JavaScript?

Question

In Python, you can do that:

arr = [1,2,3]
arr[-1] // evaluates to 3

But in JS, you can\'t:

let arr = [1,2,3];
arr[-1]; // e         


        

Answer 1

Use .slice(-N)[0]:

const array = [1, 2, 3]

console.log(array.slice(-1)[0])  // 3
console.log(array.slice(-2)[0])  // 2
console.log(array.slice(-3)[0])  // 1

In Strings you have another option (instead of [0]).

const string = 'ABC'

console.log(string.slice(-1))      // 'C'
console.log(string.slice(-2, -1))  // 'B'
console.log(string.slice(-3, -2))  // 'A'

Or using .substr(-N, 1):

const string = 'ABC'

console.log(string.substr(-1))     // 'C'
console.log(string.substr(-2, 1))  // 'B'
console.log(string.substr(-3, 1))  // 'A'