How to use fn-name - 3 common examples

properties = properties.map(property => {
      if (typeof property === 'string') { // simple index
        return { key: property, value: true };
      } else if (typeof property === 'function') { // computed index
        let key = fnName(property);
        if (!key) throw new Error('Invalid index definition: computed index function cannot be anonymous. Use a named function or set the displayName function property.');
        return { key, value: property };
      } else {
        throw new Error('Invalid index definition');
      }
    });
    return properties;

export function runValidators(value, validators) {
  let failedValidators;
  for (const validator of validators) {
    if (!validator(value)) {
      if (!failedValidators) {
        failedValidators = [];
      }
      failedValidators.push(fnName(validator));
    }
  }
  return failedValidators;
}

let name = type => typeof type === 'string'
  ? type : type.displayName || fnName(type) || ''