readonly middleware

[zuhorer]

I just created a readonly middleware

import { IMiddlewareHandler } from "mobx-state-tree";

type ForceWriteWrapper = (fn: () => void) => void;

const createReadonlyMiddleware = (): [IMiddlewareHandler, ForceWriteWrapper] => {
  let writeLock = 0;

  const middleware: IMiddlewareHandler = (call, next) => {
    if (writeLock <= 0) {
      throw new Error(`tried to invoke action '${call.name}' over a readonly node`);
    } else {
      return next(call);
    }
  };

  const forceWrite: ForceWriteWrapper = (fn) => {
    try {
      writeLock++;
      fn();
    } finally {
      writeLock--;
    }
  };

  return [middleware, forceWrite];
};
usage:

const [readonlyMiddleware, forceWrite] = createReadonlyMiddleware();
addMiddleware(node, readonlyMiddleware);

node.setX(12345); // will throw
node.child.setX(12345); // will throw

// if a change wants to be made
forceWrite(() => {
  node.setX(1234);
  node.child.setX(12345);
});

do you think it would be useful to you / should be in mst-middlewares?