array manipulator - fundamentals

function solve3(arr, commands) {
    let newArr = [];
    for (let el of commands) {
        let [command, index, element] = el.split(' ');
        switch (command) {
            case 'add':
                arr.splice(index, 0, +element);
                break;
            case 'addMany':
                let currentEl = 0;
                let removeFirst = el.split(' ');
                for (let i = removeFirst.length - 1; i >= 2; i--) {
                    currentEl = removeFirst[i];
                    arr.splice(index, 0, +currentEl);
                }
                break;
            case 'contains':
                // if (arr.indexOf(+index) !== -1) {
                //     console.log('0');
                // } else {
                //     console.log('-1');
                // }
                console.log(arr.indexOf(+index));
                break;
            case 'remove':
                arr.splice(index, 1);
                break;
            case 'shift':
                let position = +index;
                for (let i = 0; i < position; i++) {
                    let firstEl = arr.shift();
                    arr.push(firstEl);
                }
                break;
            case 'sumPairs':
                // if (arr.length % 2 === 0) {
                    let els = arr.reduce(function(total, el, index) {
                        if (index % 2 === 0) {
                            total.push(+arr[index] + (+arr[index + 1] || 0));
                        }
                        return total;
                    }, []);
                    arr = els;
                // }
                break;
            case 'print':
                for (let el of arr) {
                    newArr.push(el);
                }
                break;
        }
    }
    // console.log(newArr);
    console.log('[ ' + newArr.join(', ') + ' ]');
}