Change text field direction by javascript

Hello everyone , 

I was trying to use javascript for hiding and showing few fields and it works very well , but at the same time i tried to add a syntax to change the text direction but it didn't work !

Any one can help ? 

This is my code : 

if ( event.target.isBoxChecked(0)) {
    this.getField("Date").display = display.visible;
    this.getField("Text-1").display = display.visible;
    this.getField("Text-2").display = display.visible;
    this.getField("Name").display = display.visible;
    this.getField("Date-a").display = display.hidden;
    this.getField("Text-4").display = display.hidden;
    this.getField("Name-a").display = display.hidden;
} else {
    this.getField("Date").display = display.hidden;
    this.getField("Text-1").display = display.hidden;
    this.getField("Text-2").display = display.hidden;
    this.getField("Name").display = display.hidden;
    this.getField("Date-a").display = display.visible;
    this.getField("Text-4").display = display.visible;
    this.getField("Name-a").display = display.visible;
    this.getField("Text").direction = rtl;
}