定義后無法將javascript變數設定回null-有解無憂

我想在selectedColumnIndex每次使用后將變數設定回 null 。

我需要能夠檢查selectedColumnIndex每次使用后是否設定了新值。它可以連續使用一次或數十次（用于表格樣式 UI 組件中的“剪切和插入”功能）。

如果我在變數處放置瀏覽器斷點var check，selectedColumnIndex將顯示為null. 但是，如果在沒有$(document).on('click', '.columnUpdatesInsert', function () { }運行的情況下再次運行，將恢復到以前的值。 $(document).on('click', '.columnUpdates', function () { }selectedColumnIndex

var selectedColumnIndex = null;
$(document).on('click', '.columnUpdates', function () {
    selectedColumnIndex = $(this).attr("data-columnindex");
});

$(document).on('click', '.columnUpdatesInsert', function () {
    if (selectedColumnIndex != null) {
        // get variables from click element etc.

        $(updateColumnPosition(tableId, selectedColumnIndex, newColumnIndex));
    }
    else {
        alert("No column was selected to move.");
    }
});

function updateColumnPosition(tableId, selectedColumnIndex, newColumnIndex) {
    $.ajax({
        type: "POST",
        url: "/Task/UpdateColumnIndex",
        data: { projectId: _projectId, tableId: tableId, selectedColumnIndex: selectedColumnIndex, newColumnIndex: newColumnIndex },
        dataType: 'json',
        success: function (data) {
            if (data.success) {
                // do other unrelated work

                selectedColumnIndex = null; // this successfully sets it to null, but it is getting set back to the previous value before this code is explicitly setting it again. 
                var check = 0;
            }
            else {
                // handle error
            }
        },
        error: function (xhr, ajaxOptions, thrownError) {
            alert(xhr.status   " "   thrownError);
        },
    });
}

uj5u.com熱心網友回復：

可能是因為您將 selectedColumnIndex 作為 arg 傳遞給函式，它成為該函式的本地函式。

嘗試不要將值 selectedColumnIndex 作為 arg 傳遞，并始終將其用作全域。

var selectedColumnIndex = null;
$(document).on('click', '.columnUpdates', function () {
    selectedColumnIndex = $(this).attr("data-columnindex");
});

$(document).on('click', '.columnUpdatesInsert', function () {
    if (selectedColumnIndex != null) {
        // get variables from click element etc.

        $(updateColumnPosition(tableId, newColumnIndex));
    }
    else {
        alert("No column was selected to move.");
    }
});

function updateColumnPosition(tableId, newColumnIndex) {
    $.ajax({
        type: "POST",
        url: "/Task/UpdateColumnIndex",
        data: { projectId: _projectId, tableId: tableId, selectedColumnIndex: selectedColumnIndex, newColumnIndex: newColumnIndex },
        dataType: 'json',
        success: function (data) {
            if (data.success) {
                // do other unrelated work

                selectedColumnIndex = null; // this successfully sets it to null, but it is getting set back to the previous value before this code is explicitly setting it again. 
                var check = 0;
            }
            else {
                // handle error
            }
        },
        error: function (xhr, ajaxOptions, thrownError) {
            alert(xhr.status   " "   thrownError);
        },
    });
}

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標籤：javascript jQuery

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