Generate check digit for UPC-A

UPCcheckDigit.js

function checkDigit(bc) {
    while (bc.length < 11) {
        bc = "0"+bc;
    }

    if (bc.length > 11) {
        return bc;
    }

    var osum = 0;
    var esum = 0;

    for (var i = 0; i < bc.length; i+=2) {
        osum = osum+parseInt(bc[i]);
    }

    for (var j = 1; j < bc.length; j+=2) {
        esum = esum+parseInt(bc[j]);
    }
    
    var checkZero = (((osum*3) + esum) % 10);
    
    if (checkZero !==0) {
        var check = (10-checkZero).toString();
        return bc+check;
    } else {
        return bc+"0");
    }
}