How to use the JS API Range to select plain text instead of tag

DIV Image

This is a 'contentEditable = true'DIV, there are pictures in DIV with plain text, These plain text is not wrapped in any tag, and I need to select a text by code, but If the DIV is all tags, the "Range.setStart ()" method must provide an NODE as a parameter It will be very simple, but now I do not know how to choose these plain text. What I want to do is click on a button to remove the contents of the DIV from the back