JavaScript Function that returns a Promise or Callback depending if a callback was specified

functionPromiseAndCallback.js

function myFunc(obj, callback) {                                     // call back is an optional param
    if (!callback) {                                                 // if callback omitted, we return a promise
        const performWork = async () => obj                          // this simulates work being done before resolving
        return new Promise(async (resolve, reject) => {              // return an async promise wrapper
            const value = await performWork()                        // do the work
            resolve(value)                                           // resolve the promise
        })
    }
    const cb = obj                                                   // if callback present, we return it
    callback(cb)
}

const test = { test: 1337 }                                          // this is the sample data that comes in as obj

// Promise version
myFunc(test).then((res) => console.log('Promise version', res))      // demonstration as promise

// Callback version
myFunc(test, (res) => {                                              // demonstration as callback        
    console.log('Callback version', res)
})