document.getElementById("Q9_select").innerHTML = (function () {
    let str = "";
    for (var i = 0; i <= 9; i++) {
        str += !i ? "<option value=''> " + "選択してください" + "</option>\n" : "<option value=" + i + ">" + i + "の段</option>\n";
    }
    return str;
})();
document.getElementById("Q9_select").addEventListener("change", function (e) {
    let Q = this.value ? this.value : 0;
    let str = "";
    let view_flg = 1;
    for (var i = 1; i <= 9; i++) {
        let ans = Q * i;
        str += "<p class='h2'><span class='text-primary'>" + Q + "</span> × " + i + "= <span class='Q9_ans' style='visibility:visible'>" + ans + "</span></p>";
    }
    str += "<p class='text-center'><button class='h2 btn btn-primary' id='view'>九九の解を<span id='txt'>非表示に</span>する</button></p>";
    document.getElementById("Q9_view").innerHTML = str;
    document.getElementById("view").addEventListener("click", function () {
        let object = document.getElementsByClassName("Q9_ans");
        for (const key in object) {
            if (Object.hasOwnProperty.call(object, key)) {
                const element = object[key];
                element.style.visibility = view_flg ? "hidden" : "visible";
            }
        }
        view_flg = view_flg ? 0 : 1;
        document.getElementById("txt").innerText = view_flg ? "非表示に" : "表示";
    });
});