Keeping the structure intact in contentEditable Div

I am trying to build a Rich Text Editor from scratch, Seems like a really big & complex task, I know, The editor should make use of Range & selection apis instead of execCommand, be extensible and support basic editing features like paragraph alignment and inline styling.

I've found the SlateJs library which also allows you to build rich text editor. However I am determined to do this from scratch, even though I don't know where to start.

The problem is that when the user types into my editor the text goes directly into container element with contentEditable div. However when the user types into SlateJs editor, The text goes into a three nested spans which are contained inside a paragraph element , You can inspect this here https://www.slatejs.org/examples/richtext

How can I implement this behavior ?

preventDefault doesn't work on input but works on keydown

editor.addEventListener("keydown",(e)=> {
     e.preventDefault()
    // if the key is a printable character
    if(event.key.length == 1){
        // this always appends to the last of paragraph even if the cursor is somewhere else
        this.topLevelParagraph.innerHTML += event.key
    }
})

The caret position doesn't change, Text always goes at last.

• What's the best way to fix this issue.
• I would appreciate if you could recommend articles or resources that can help me build a library like slatejs, rich text editor

I learned that to maintain structure, You need to do some things

1 - Initial structure, You must create initial elements, wrappers and formatting inline elements and decide which element should / will take input from the user

2 - A keydown event on the container with contentEditable attribute , Now you can preventDefault on the event and put the key into the exact element inside the container, You must filter out keys that are not printable characters, You can filter control characters using ascii codes but I recommend you use unicode<br>
I used e.key.length == 1 and some other filters

3 - Now your input has gone into the box, or maybe not because you preventedDefault, You must also track user selection range and adjust it after every key, so input is at the right position, for example on each key you must collapse the current range at endPosition + 1, so the caret remains right next to the current letter typed

4 - You must handle copy paste, You don't have to handle backspace key, However after every user action, You must make sure the structure remains intact

You could go a separate way and create your own data structure, You take all the events from the browser and have a structure in your code that user changes instead of the text field and re render the object that takes the input / has changed.