Fun TypeScript challenge

funTypeScriptChallenge.ts

/*
 * TypeScript challenge for anyone to flex their TS dev skills
 * 
 * Write a function wrapper that accepts any arbitrary function with arbitrary arguments. 
 * This wrapper should output a new function that is a modified version of the original one. 
 * This new function should have an extra argument which is last in the list of arguments. This argument is boolean and optional, named "verbose". 
 * This new function works exactly like the original one, with the exception that it should output "verobse is on!" when
 * "verbose" argument is set to true.
 */
 
 // Solution is down below
 
 
 
 
 
 
 
 
 
 
 
 
 
 
// Answer function
function extend<T extends unknown[], R extends any>(
    fn: (...args: T) => R
) {
    return (...params: [...args: T, verbose?: boolean]) => {
        const hasVerboseParam = params.length === fn.length + 1;

        if (hasVerboseParam) {
            const verbose = params[params.length - 1];
            if (verbose) console.log('verbose is on!');
            return fn(...(params.slice(0, -1) as T));
        } 

        return fn(...(params as unknown as T));
    };
}


// Test function to wrap
const meow = (n: number, s?: string) => {
    let result = n.toString();
    if (s) {
        result += ' ' + s.toUpperCase();
    }

    return result;
}

const verboseMeow = extend(meow);

const CAT_LIVES = 9;
let testSuccessful = true;

if (testSuccessful) testSuccessful = verboseMeow(CAT_LIVES, 'lives', true) === `${CAT_LIVES} LIVES`; // 1 verbose output

if (testSuccessful) testSuccessful = verboseMeow(CAT_LIVES, 'lives') === `${CAT_LIVES} LIVES`;       // no verbose output 

if (testSuccessful) testSuccessful = verboseMeow(CAT_LIVES) === CAT_LIVES.toString();                // no verbose output

console.log(testSuccessful ? 'Everything works' : 'There is an error');