How do I concat a string and an int and find its value in an array?

Question

See the final codebase below. My initial approach of trying to use an array as an object was incorrect.

I'm trying to concat a string and int to look up a particular item in an array arr. The current code base console logs undefined.

Can someone explain why undefined is console logged?

Codebase in question:

const a = "T";
const b = 2;
const c = a + b;

let arr = [
        T0: 0,
        T1: 1,
        T2: 1
    ];

console.log(arr.find(e => e == c));

Thank you.

More detail (not necessary to read):

I'm trying to write code to provide an answer for an n-th Tribonacci number when inputted n.

Psuedo-code:

var tribonacci = function(n) {
  
    let arr = [
        T0 = 0;
        T1 = 1;
        T2 = 1;
    };
    
    for (i = 0; i < n + 1; i++) {
        let ("T" + (i + 3)) = ("T" + i) + ("T" + (i + 1)) + ("T" + (i + 2))
        arr.push("T" + (i + 3));
    }
    
    return arr.find(e => e == ("T" + (n + 3));

Final codebase:

Thank you, Everyone, for the feedback.

I removed the "values" in the array because there are no keys & values arrays.
I removed the .find() method and added a simpler way to lookup n via arr[n].

var tribonacci = function(n) {
  
    let arr = [0, 1, 1];
    
    for (i = 0; i < n - 2; i++) {
        let add = arr[i] + arr[i + 1] + arr[i + 2]
        arr.push(add);
    }
    
    return arr[n]
};

The array doesn't contain the strings, it just contains the integers. — Barmar, Nov 04 '20 at 23:34
`let arr = [ T0 = 0, T1 = 1, T2 = 1 ];` is odd syntax, it just creates an array `[0,1,1]` and creating 3 global variables, T0,T1 and T2 that are unconnected from the Array - I think you need a refresher course in Javascript syntax — Jaromanda X, Nov 04 '20 at 23:34
you'll also see an error for the line `let ("T" + (i + 3)) =` — Jaromanda X, Nov 04 '20 at 23:35
I just got it. He doesn't expect the array to contain the strings, he's expecting `c` to contain the value of `T2`. — Barmar, Nov 04 '20 at 23:36
You need to cover at least the basics of the language. You are using nonexistent syntax. — PM 77-1, Nov 04 '20 at 23:38
May be defining an object is better in this case. Your array contains only the integers. — BlackMath, Nov 04 '20 at 23:38
You don't need `find()` with an object, you just use `arr[c]` — Barmar, Nov 05 '20 at 00:37

score 1 · Accepted Answer · answered Nov 04 '20 at 23:40

Perhaps this code will help (I may be out by one on the index, but you can fix that)

var tribonacci = function(n) {
    let arr = [0, 1, 1];
    for (i = 2; i < n; i++) {
        arr.push(arr.slice(-3).reduce((a,b) => a+b));
    }
    return arr[n];
};
console.log(tribonacci(1))
console.log(tribonacci(2))
console.log(tribonacci(3))
console.log(tribonacci(4))
console.log(tribonacci(7))
console.log(tribonacci(14))

How do I concat a string and an int and find its value in an array?

1 Answers1