improve javascript stacktrace

validation.js

function getName () {
    return new Promise((resolve)=>{
        resolve({status:500});
    }).then((response) => {        // validate output
        if (response.status === 500){
            throw new Error('request to get name has failed');
        }else{
            return response;
        }
    }); // emulate http call
}

function getFullName (info) {
    if (!info){ // validate input
        throw new Error('info is missing');
    }
    return new Promise((resolve) => {
        resolve(info.firstName + ' ' + info.lastName)
    })
}

function countLetter(fullName, letter){
    if (!fullName || !letter){ // validate input
        throw new Error('letter or fullName is undefined fullName=[' + fullName + '] letter=[' + letter + ']');
    }
    return new Promise((resolve)=>{
        resolve(fullName.split(letter).length-1);
    })
}
function countLetters (fullName) {
    if (!fullName){ // validate input
        throw new Error('fullName is missing');
    }
    const result = {};
    return Promise.all('abcdefghijklmnopqrstuvwxyz'.split('').map((char)=>{
        countLetter(fullName, char).then((count)=>{
            result[char] = count;
        })
    })).then(()=>result);
}