introduction
The at() method in Array takes an int value as a parameter and returns the element of the given position(index) in the araay.
If there is no data by int value, it returns undefined.
Examples
const foo = ["a", "b", "c" , "d", "e"]
console.log(foo.at(0)) // "a"
console.log(foo.at(-1)) // "e"
console.log(foo.at(7)) // undefined
console.log(foo.at()) // "a"
The at() method plays same role as bracket notation [] in Array (array[int]).
Moreover, The at() method can have not only positive but also negative integer value. It's same as array[array.length - integer value].
The at() method can be passed empty. In this case, it will return first element. Shortly, it means default is 0)
Differences
You may get a questions why at() method is developed if it's same as [] in array.
The big difference between at() method and [] is you cannot assign element by index.
const fruits = ['apple', 'banana', 'orange']
fruits.at(0) = 'pineapple' // No!
fruits[0] = 'pineapple'
The at() method will cause Invalid assignment target error.
The other difference is that the at() method can have negative integer to get element from end of list.
const fruits = ['apple', 'banana', 'orange']
console.log(fruits.at(-1)) // "orange"
console.log(fruits[-1]) // "undefined"
If you use negative integer in [], you will get undefined.