为了更好地理解tabindex元素是如何工作的，完成公认的回答:

The tabindex global attribute is an integer indicating if the element can take input focus (is focusable), if it should participate to sequential keyboard navigation, and if so, at what position. It can take several values:   -a negative value means that the element should be focusable, but should not be reachable via sequential keyboard navigation;   -0 means that the element should be focusable and reachable via sequential keyboard navigation, but its relative order is defined by the platform convention;   -a positive value means should be focusable and reachable via sequential keyboard navigation; its relative order is defined by the value of the attribute: the sequential follow the increasing number of the tabindex. If several elements share the same tabindex, their relative order follows their relative position in the document.

来自:Mozilla开发人员网络

我在github上找到了select2的解决方案

https://github.com/ivaynberg/select2/issues/1436

对于bootstrap 3，解决方案是:

$.fn.modal.Constructor.prototype.enforceFocus = function() {};

Bootstrap 4重命名了enforceFocus方法为_enforceFocus，所以你需要修补它:

$.fn.modal.Constructor.prototype._enforceFocus = function() {};

从以上链接复制的解释:

Bootstrap向focusin事件注册了一个监听器，它检查被聚焦的元素是覆盖本身还是它的后代——如果不是，它只是重新聚焦在覆盖上。随着select2下拉框被附加到正文，这有效地防止你在文本框中输入任何东西。 您可以通过覆盖在模态上注册事件的enforceFocus函数来快速修复这个问题

如果你使用jquery移动弹出窗口，你必须重写_handleDocumentFocusIn函数:

.mobile.popup.prototype美元。_handleDocumentFocusIn =函数(e) { If ($(e.c target).close ('.select2-dropdown').length)返回true; ｝

在页面上使用此代码

$(function () {
    $(".select2").select2({
        dropdownParent: $('#myModal')
    });

    $("#myModal").on('change', '#vdn_number', function () {
        var term = $(this).val();
        ajax: ({
            url: "getAjaxData/",
            dataType: 'json',
            type: "POST",
            data: function (term, page) {
                return {
                    q: term, // search term
                    col: 'vdn'
                };
            },
            results: function (data) { // parse the results into the format expected by Select2.
                // since we are using custom formatting functions we do not need to alter remote JSON data
                return { results: data };
            }
        });
    });
});

我想这对你有帮助

你可以在$(文档)中再次调用select2 trigger

$(".select2").select2({ 
                width: '120' 
            });

在我的情况下，我有两个情态动词同样的问题，所有都解决了使用:

$('.select2').each(function() { 
    $(this).select2({ dropdownParent: $(this).parent()});
})

正如在项目问题#41中，一个用户说。