TextRange save/restore

i want to make a highlight script in js. the first part, coloring the selection is preety straightforward, i create a textrange from the selection and issue a execCommand(“backcolor”,… now i want to save this selection into a database and restore it later when the user visits the page again. there is just one problem. i can`t get the coordinates for textrange.moveStart() and textrange.moveEnd() for the selection. can somebody tell me how can i get those values? or maybe you can tell me an alternate way to do the text coloring so i can put it back later. Please help

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