Transform generic objects with type guargs only

transform.ts

import { keys } from 'ts-transformer-keys';

export type ConvertibleToNumber<T> = {
    [K in keyof T]: number | string;
};

function isNumeric(value: string): boolean {
    return isFinite(parseFloat(value));
}

function isComplete<T>(obj: any): obj is T {
    const prototypeKeys = keys<T>();
    for (const key of prototypeKeys) {
        if (obj[key] === undefined) {
            return false;
        }
    }
    return true;
}

function convertStrings<T extends Record<string, string>>(
    input: T
): ConvertibleToNumber<T> {
    const output: Partial<ConvertibleToNumber<T>> = {};

    for (const key in input) {
        const value = input[key];
        if (!value) {
            continue;
        }
        if (isNumeric(value)) {
            output[key] = parseFloat(value);
        } else {
            output[key] = value;
        }
    }

    if (!isComplete<ConvertibleToNumber<T>>(output)) {
        throw new Error('Something went wrong');
    }

    return output;
}

const data = {
    name: 'John',
    age: '25',
};

const convertedData = convertStrings(data);
console.log(convertedData); // { name: 'John', age: 25 }