A. Conceptos básicos
const arr = ["mx", "my", "mu"]
console.log(arr)
console.log(arr.length)
console.log(arr[0])
console.log(arr[1])
console.log(arr[2])
arr[2] = "hi"
const i = 0
console.log(arr[i])
arr[i] = "ho"
console.log(arr[i])
Salida
[ 'mx', 'my', 'mu' ] 3 mx my mu mx ho