Question

我试图创建一个简单的JS类，然后尝试创建一个对象，但是在标记的行中它表示＆＃34;无法读取属性＆＃39; show＆＃39;未定义＆＃34;。

function DashboardNumberItem(dashboardItemId, dataUrl) {
    this.dashBoardItem = $("#" + dashboardItemId);
    this.dataurl = dataUrl;
    this.placeholder = $("#" + dashboardItemId + " .number-placeholder");
    this.dashBoardItem.hide();
}

DashboardNumberItem.prototype.loadData = function() {
    $.ajax({
        url: this.dataurl,
        method: 'GET',
        dataType: 'json',
        success : function(data) {
            this.dashBoardItem.show(); // this.dashBoardItem is undefined?!
            this.placeholder.text(data);
        }
    });
};

var dashboardItem = new DashboardNumberItem("dashboard-item-vardhandelseimportcount", "/Controller/Action");
dashboardItem.loadData();

为什么会发生这种情况？如何才能使其发挥作用？

Answer 1

this可能不是您期望的那样，并且将指向 jQuery的XMLHttpRequest对象而不是您的DashboardNumberItem实例，所以设置一个新变量，例如var that = this;

DashboardNumberItem.prototype.loadData = function() {
    var that = this; // set up a reference to capture it
    $.ajax({
        url: that.dataurl,
        method: 'GET',
        dataType: 'json',
        success : function(data) {
            that.dashBoardItem.show(); // which you can now use in another context
            that.placeholder.text(data);
        }
    });
};

如何创建简单的JavaScript＆＃34; class＆＃34;？

1 个答案: