function hikaku_allcheck() {
    var ElementsCount = document.hikakuform.elements['hikaku_items[]'].length;
    for(i = 0; i < ElementsCount; i++) {
        document.hikakuform.elements[i].checked = true;
    }
}

function hikaku_alluncheck() {
    var ElementsCount = document.hikakuform.elements['hikaku_items[]'].length;

    for (i = 0; i < ElementsCount; i++) {
        // trueとfalseを反転
        if (document.hikakuform.elements[i].checked == true) {
            document.hikakuform.elements[i].checked = false;
        } else if (document.hikakuform.elements[i].checked == false) {
            document.hikakuform.elements[i].checked = true;
        }
    }

    document.hikakuform.submit();
}

function mysubmit() {
    var ElementsCount = document.hikakuform.elements['hikaku_items[]'].length;
    var CheckedCount = 0
    for (i = 0; i < ElementsCount; i++) {
        if (document.hikakuform.elements[i].checked == true) {
            CheckedCount++;
        }
    }
    if (CheckedCount < 2) {
        alert("２つ以上の比較したい商品にチェックをつけてください")
    } else {
        document.hikakuform.submit();
    }
}