array manipulator

function  solve(arr, commands){

    for (let i = 0; i < commands.length; i++) {

        let args = commands[i].split(' ');

        switch (args[0]){
            case 'add':
                let index = Number(args[1]);
                let number = Number(args[2]);
                arr.splice(index, 0, number);
                break;
            case 'addMany':
                let index1 = Number(args[1]);
                let numbers = args.slice(2);
                arr.splice(index1, 0, ...numbers);
                break;
            case 'contains':
                let contains = Number(args[1]);
                if (contains){
                    let index = arr.indexOf(contains);
                    console.log(index);
                } else {
                    console.log(-1);
                }
                break;
            case 'remove':
                let remove = Number(args[1]);
                arr.splice(remove, 1);
                break;
            case 'shift':
                let shift = Number(args[1]);
                for (let j = 0; j < shift; j++) {
                    let digit = arr.shift();
                    arr.push(digit);
                }
                break;
            case 'sumPairs':
                let newArr = [];
                if (arr.length % 2 === 0) {
                    for (let k = 0; k < arr.length; k += 2) {
                        newArr.push(arr[k] + arr[k + 1]);
                    }
                } else {
                    for (let k = 0; k < arr.length - 1; k += 2) {
                        newArr.push(arr[k] + arr[k + 1]);
                    }
                }
                arr = newArr;
                break;
            case 'print':
                console.log(`[ ${arr.join(', ')} ]`);
                break;
        }

    }
}