JavaScript报错，TypeError: this._setPara is not a function

下是一段获取元素位置，并通过判断index值，使其向左或向右运动的代码局部。在运行过程中报错，this._setPara is not a funtion...百思不得其解，请各位指教~多谢~

  _setPara : function(){
            this._b = this.swContainer.css("left");
            this._move();
        },
        moveLeft : function(){
            this._setPara();
            this.index++;
            if(this.index == this.swCounter){
                setTimeout(this.moveRight, this.swDuration);
            }else{
                setTimeout(this.moveLeft, this.swDuration);
            }
        },
        moveRight : function(){
            this._setPara();
            this.index--;
            if(this.index == 0){
                setTimeout(this.moveLeft, this.swDuration);
            }else{
                setTimeout(this.moveRight, this.swDuration);
            }
        },