Make json snapshots less painful: replace functions/classes with their names (if possible), convert dates to numbers, remove undefined enumerable properties

test-utils-json.js

function logObject(obj) {
  let result = JSON.stringify(obj, null, 2);
  let hr = '';
  for (let i = 0; i < 80; i++) { hr += '-'; }
  const lines = result.split('\n');
  result = lines.map(line => line.replace(/^(\s+)"([a-zA-Z0-9_$]*)"/, '$1$2')).join('\n');
  console.log(`${hr}{{{\n${result}\n}}}${hr}`);
}

function stringifyComplexObjects(obj) {
  JSON.stringify(obj, (key, value) => {
    if (typeof value === 'object' && value && Object.keys(value).length > 0) {
      Object.keys(value).forEach((iterKey) => {
        const iterVal = value[iterKey];
        if (typeof iterVal === 'function') {
          // this is kinda fuzzy, decorators may mess this up, so don't expect wonders
          const subType = iterVal && iterVal.prototype && iterVal.prototype.constructor && /^\s*class/.test(iterVal.toString()) ? 'class' : 'function';
          value[iterKey] = subType + (iterVal.name ? `:${iterVal.name}` : '');
        } else if (iterVal instanceof Date) {
          value[iterKey] = iterVal.getTime();
        } else if (iterVal === undefined) {
          delete value[iterKey];
        }
      });
    }
    return value;
  });
  return obj;
}