Safe stringify (avoid circular reference)

safeStringify.js

// borrowed from https://stackoverflow.com/questions/11616630/json-stringify-avoid-typeerror-converting-circular-structure-to-json/48254637#48254637
const safeStringify = v => {
  const cache = new Set();
  return JSON.stringify(v, (key, value) => {
    if (typeof value === 'object' && value !== null) {
      if (cache.has(value)) {
        // Circular reference found, discard key
        return;
      }
      // Store value in our set
      cache.add(value);
    }
    return value;
  });
};