create a unique variable from a string inside loop [duplicate]

Question

I am trying to use a key (unique number) and add a letter to that key (cause you cant just do var 230 = []). so I can push the right value to the right array. How can I do that??? ):

const keys = [230, 330]

let a230 = []
let a330 = []
keys.forEach((key, value) => {
   a[key].push(value) //push value to a230...
}
)