全局作用域-在触发事件侦听器后访问“this”

我有一个使用XHR上传文件的mootools类:

var foo = new Class({

    initialize: function() {

        this.bar = 'value';
    },

    upload: function() {

        // This method uploads a file

        ….
        xhr.addEventListener('load', this.uploadComplete, false);
        ….

    },
    uploadComplete: function() {

        // Is getting called on completion of file upload       

        console.log(this.bar); // undefined, but I want to to be 'value'
    }


});

我想访问 this.bar 在 uploadComplete 方法,但是 this 没有通过 xhr.addEventListener('load', this.uploadComplete, false);

任何帮助都将不胜感激。