javascript - CategorySelect 不是构造函数

Question

我正在尝试让一个多选的 jsfiddle 工作，但我在控制台中收到一个错误:

CategorySelect is not a constructor

为什么我的 CategorySelect 不是构造函数？

代码:

var CategorySelect = (function() {
    function CategorySelect() {
        var _this = this;
        this._configureMultiselect = function() {
            _this._multiselectConfiguration = {
                buttonWidth: '100%',
                buttonContainer: '<div style="height: 64px;" />',
                buttonClass: 'none',
                nonSelectedText: "select category",
                includeSelectAllOption: true,
                disableIfEmpty: true,
                onSelectAll: function() {
                    if (!$("#category-div span.multiselect-selected-text").text()) {
                        $("#category-div span.multiselect-selected-text").text('Select category');
                    }
                },
                onChange: function(option, checked) {
                    _this._selectedCategories = ko.observableArray([]);
                    var self = _this;
                    $('#category-select option:selected').each(function() {
                        self._selectedCategories.push(($(this).text(), $(this).val()));
                    });
                    console.log(_this._selectedCategories());
                }
            };
        };
        this._instantiateCategories = function() {
            _this._categories = ko.observableArray([
                new Category("Vegan Meat", 1),
                new Category("Vegan Dairy", 2),
                new Category("Confectionary", 3),
                new Category("Baking", 4),
                new Category("Dessert", 5),
                new Category("Restaurants", 6),
                new Category("Grocers", 7)
            ]);
        };
        this._configureMultiselect();
        this._instantiateCategories();
        $("#category-select").multiselect(this._multiselectConfiguration);
    }
    return CategorySelect;
})();

Here is the jsfiddle

Answer 1

声明是 hoisted到 JavaScript 范围的顶部，但绝不是它们的赋值。

当你引用 CategorySelect 时，它还没有被设置为任何东西，就像在包含范围的顶部有一个 var CategorySelect;，领先其值为 undefined，因此不是构造函数。

jsFiddle .