How to update widget value after user change vaue in othe input widgets

Q&A
1

I have a page will 4 input widgets, 3 is enable, 1 is not.

User will input the 3 widget, and the simple string combination will fill the fourth widget.

I make a simple JavaScript expression to combine the 3 string into 1 and set it to the value properties of the fourth widget.

However, when I run, and input the value to 3 input widgets, the value of the fourth widget is not updated.

What step should I add for it to work?

 

EDIT: it is OK now.I made a mistake of calling the vale of the input without adding "$data." in the front.

 

2

it is OK now.I made a mistake of calling the vale of the input without adding "$data." in the front.