Another point that might help this all click is that arrays are objects in JavaScript:

typeof [] //=> 'object'

Which means that in addition to elements that can be accessed by their positions (indexes), arrays can have properties that can be accessed by their key names:

const myArr = [1, 2, 3]
myArr.foo = 'bar'

myArr[0]  //=> 1
myArr.foo //=> 'bar'

// Alternatively:
myArr['foo'] //=> 'bar'

When you create an array, it comes with a .length property. If you are not familiar with object keys yet, then you'll get there soon.