链式长取值

分享一个链式长取值的function ，代替可选链 。

// 链式长取值
    get(source, path, defaultValue = undefined) {
      const paths = path.replace(/\[(\d+)\]/g, '.$1').split('.')
      let result = source
      for (const p of paths) {
        result = Object(result)[p]
        if (result === undefined) {
          return defaultValue
        }
      }
      return result
    },