XHR2 在 Collection 中的访问事件

Question

我有一个集合，它使用 XMLHttpRequest 成功地将文件发送到服务器。 但我不知道如何将函数附加到 XHR2 事件。

它似乎只在代码直接位于 send() 内部时才有效：

var Photos = Backbone.Collection.extend({
    url: config.url,

    /**
     * Send file to server.
     * @todo Should Backbone.sync be overwritten instead?
     */
    send: function (file) {
        var data = new FormData(),
            xhr = new XMLHttpRequest();

        // ======> Doesn't work:
        xhr.addEventListener('load', this.onLoad(xhr));

        // ======> Doesn't work either:
        xhr.onload = this.onLoad(xhr);

        // ======> But this works:
        xhr.onload = function () {
            var response = $.parseJSON(xhr.responseText);
            console.log(response); // Works!
        };

        data.append('file', file);

        xhr.open('POST', this.url);
        xhr.send(data);
    },

    /**
     * Respond to XHR2 'onload' event.
     */
    onLoad: function (xhr) {
        var response = $.parseJSON(xhr.responseText);
        console.log(response); // Doesn't work!
    }

});

为什么会这样？如何将代码移出 send() 并放入单独的函数中？

Answer 1

所以，感谢Musa 和Jonathan Lonowski，我现在有了以下工作代码：

var Photos = Backbone.Collection.extend({
    url: config.url,

    /**
     * Send file to server.
     * @todo Should Backbone.sync be overwritten instead?
     */
    send: function (file) {
        var data = new FormData(),
            xhr = new XMLHttpRequest();

        xhr.addEventListener('load', this.onLoad);

        data.append('file', file);

        xhr.open('POST', this.url);
        xhr.send(data);
    },

    /**
     * Respond to XHR2 'onload' event.
     *
     * No need to pass in the xhr object, since addEventListener
     * automatically sets 'this' to 'xhr'.
     */
    onLoad: function () {
        var response = $.parseJSON(xhr.responseText);
        console.log(response); // Works now!
    }

}); 

Answer 2

您使用this.onLoad(xhr) 调用函数，而不是传递函数引用。试试

var self = this;
xhr.onload = function () {
    self.onLoad(xhr);
};