Synchronous callbacks in javascript

Question

Right, just so it's out the way, I'm new to JS and Espruino and so got stuck during a project; I'm trying to get the max of an array to be console.logged just after the main function is executed:

const cw = 1;
const ccw = 0;
const dataCW = [];
const peekCW = [];
const dataCCW = [];
const peekCCW = [];
const dataLength = 36;


const getData = (dir, t, fn) => {
    const solarIn = () => analogRead(A5);
    const dataRead = () => ((solarIn() * 65536) * 5.0) / 65536;
    const dataPush = (data) => {
        data.push(dataRead());
    };

    const peekVal = (fnc) => {
        if(dir === 1) {
            for(let i = 0; i < dataLength; i++) {
                setTimeout(() => {
                    dataPush(dataCW);
                    if(dataCW.length === dataLength) {
                        let peekValCW = Math.max.apply(null, dataCW);
                        let peekValPosCW = dataCW.indexOf(peekValCW);
                        peekCW.push(peekValPosCW);
                    }
                }, i * (t / dataLength));
            }
        }
        else if(dir === 0) {
            for(let i = 0; i < dataLength; i++) {
                const forCCW = setTimeout(() => {
                    dataPush(dataCCW);
                    if(dataCCW.length === dataLength) {
                        let peekValCCW = Math.max.apply(null, dataCCW);
                        let peekValPosCCW = dataCCW.indexOf(peekValCCW);
                        peekCCW.push(peekValPosCCW);
                    }
                }, i * (t / dataLength));
            }
        }
        fnc();
    };
    fn(peekVal, peekCW);
};


getData(cw, 1000, (n, m) => n((m) => console.log(m)));

I feel I've spent way too much time trying on my own and only got frustrated with returns like undefined or = [ ] because I can't pass it properly after the function's done executing. Honestly I'm only interested in resolutions involving callbacks, I know Espruino now has Promises implemented and all but feel that this needs to be done with callbacks as I feel this is such an important topic to know/master. Thanks for you help.

Regards, George M.