Element implicitly has an any type because expression of type string cant be used to index type

//This will fail typecheck
const map = {};
map[someString] = "hello";

//This will pass typecheck
const map: {[key:string]: string} = {};
map[someString] = "hello";

const color : { [key: string]: any } = {
    red: null,
    green: null,
    blue: null
};

More information on indexing in TypeScript: https://basarat.gitbook.io/typescript/type-system/index-signatures

interface IObjectKeys {
  [key: string]: string | number;
}

interface IDevice extends IObjectKeys {
  id: number;
  room_id: number;
  name: string;
  type: string;
  description: string;
}

const DNATranscriber = {
    G: 'C',
    C: 'G',
    T: 'A',
    A: 'U'
};

export default class Transcriptor {
    toRna(dna: string) {
        const codons = [...dna];
        if (!isValidSequence(codons)) {
            throw Error('invalid sequence');
        }
        const transcribedRNA = codons.map(codon => DNATranscriber[codon]);
        return transcribedRNA;
    }
}

function isValidSequence(values: string[]): values is Array<keyof typeof DNATranscriber> {
    return values.every(isValidCodon);
}
function isValidCodon(value: string): value is keyof typeof DNATranscriber {
    return value in DNATranscriber;
}