jQuery fileupload.js this._on不是函数错误

Question

_initEventHandlers: function () {
        if (this._isXHRUpload(this.options)) {
            this._on(this.options.dropZone, {
                dragover: this._onDragOver,
                drop: this._onDrop,
                // event.preventDefault() on dragenter is required for IE10+:
                dragenter: this._onDragEnter,
                // dragleave is not required, but added for completeness:
                dragleave: this._onDragLeave
            });
            this._on(this.options.pasteZone, {
                paste: this._onPaste
            });
        }
        if ($.support.fileInput) {
            this._on(this.options.fileInput, {
                change: this._onChange
            });
        }

此代码在Jquery.fileupload.js中，但抛出错误：

this._on（）不是函数

我该怎么办？