@fellow/prosemirror-recreate-transform/src/getReplaceStep.ts

Create a set of steps transforming one prosemirror json document to another

import { ReplaceStep } from "prosemirror-transform";
import { Node } from "prosemirror-model";

export function getReplaceStep(fromDoc: Node, toDoc: Node) {
    let start = toDoc.content.findDiffStart(fromDoc.content);
    if (start === null) {
        return false;
    }

    let { a: endA, b: endB } = toDoc.content.findDiffEnd(fromDoc.content) as {
        a: number;
        b: number;
    };
    const overlap = start - Math.min(endA, endB);
    if (overlap > 0) {
        // If there is an overlap, there is some freedom of choice in how to calculate the
        // start/end boundary. for an inserted/removed slice. We choose the extreme with
        // the lowest depth value.
        if (
            fromDoc.resolve(start - overlap).depth <
            toDoc.resolve(endA + overlap).depth
        ) {
            start -= overlap;
        } else {
            endA += overlap;
            endB += overlap;
        }
    }

    return new ReplaceStep(start, endB, toDoc.slice(start, endA));
}