rl.clearScreenDown()

• 返回值：this

rl.clearScreenDown() 方法向内部待执行动作列表中添加一个动作，该动作用于清除从光标当前位置向下的相关流内容。除非在构造函数中传入了 autoCommit: true，否则需调用 rl.commit() 才能看到此方法的效果。

【The rl.clearScreenDown() method adds to the internal list of pending action an action that clears the associated stream from the current position of the cursor down. Call rl.commit() to see the effect of this method, unless autoCommit: true was passed to the constructor.】