Then I added a breakpoint in ButtonRender.js to check how a Button is rendered in UI5.

In below picture we can see the render sequence of the controls:

UIArea -> Shell -> UIComponent -> XMLView -> NavContainer -> PageRender -> ButtonRender

After we execute code of line 198, the button’s text is not displayed on the page, so we know that we need to debug further.

In writeEscape() function, we can see the button’s text has been pushed in a buffer.

And UI5 not calls DOM native method to draw controls one by one, UI5’s strategy is rendering a batch of controls in one UIArea one time.

But the layout is strange, it is not display as we expected. we need to debug further. I continue to debug and step over many line’s of code, the html elements’ CSS style are still not change until I go to line 9184: