modify-object.ts

type CommandFunc = (
  target: any,
  key: string,
  value: any,
  commands: Commands,
) => object;

type Commands = {
  [key: string]: CommandFunc;
};

const defaultCommands: Commands = {
  default: (target, key: string, value: any) => {
    return { [key]: value };
  },
  merge: (target, key, modifier, commands) => {
    return { [key]: modifyObject(target[key] || {}, modifier, commands) };
  },
  delete: () => ({}),
};

function splitKey(rawKey: string): [string, string] {
  const [, command, key] = /^\$(\w+)__(\w+)$/.exec(rawKey) || [
    '',
    'default',
    rawKey,
  ];
  return [command, key];
}

export function modifyObject(
  target: object,
  modifier: object,
  commands: Commands = {},
) {
  const finalCommands = { ...defaultCommands, ...commands };
  const result = { ...target };
  for (const [rawKey, value] of Object.entries(modifier)) {
    const [command, key] = splitKey(rawKey);
    const commandFunc = finalCommands[command];

    if (!commandFunc) {
      throw new Error(`Unexpected Command: '${command}'`);
    }
    const patch = commandFunc(target, key, value, finalCommands);
    Object.assign(result, patch);

    if (!patch.hasOwnProperty(key)) {
      delete result[key];
    }
  }
  return result;
}