Codecademy Sample Solution: Codeyear Write Back to the Input Field

// sample solution to script.js

function modify_qty(val) {
    var qty = document.getElementById('qty').value;
    var new_qty = qty + val;
   
    if (new_qty < 0) {
        new_qty = 0;
    }
    document.getElementById('qty').value = new_qty;
    return new_qty;
}