Example of how Flexport uses mutation-sentinel

flexport-sentinel.js

import {configureSentinel} from "mutation-sentinel";
...

// Called on initial app load, and when route changes.
function updateConfig(route) {
  if (/* mutation-sentinel enabled for route */) {
    configureSentinel({shouldIgnore, mutationHandler});
  } else {
    configureSentinel({shouldIgnore, mutationHandler: () => {}});
  }
}

// Some libraries will mutate their objects internally.
function shouldIgnore(val) {
  return (
    moment.isMoment(val) ||
    React.isValidElement(val) ||
    // Appending a File wrapped with a sentinel to FormData does not work
    (typeof File !== "undefined" && val instanceof File)
  );
}

function mutationHandler(mutation) {
  // We don't care about reporting the same exact mutation multiple times.
  if (hasSeenSentinelMutation()) {
    return;
  }
  console.warn("Mutation detected by sentinel!", mutation);
  /* Also log to Sentry (our production error tracker) */
}

const seenMutations = new Set();

function hasSeenSentinelMutation() {
  // Since the sentinel catches the mutation at the exact place in the code
  // where the mutation is executed, we can use the stack trace to uniquely
  // identify a mutation.
  const e = new Error();
  const stack = e.hasOwnProperty("stack") ? e.stack : null;
  if (stack != null) {
    const mutationHash = murmur.murmur3(stack, 0);
    if (seenMutations.has(mutationHash)) {
      return true;
    }
    seenMutations.add(mutationHash);
  }
  return false;
}