code: function dynamicLoad(dynamicOptions, options, defaultOptions) {
      let loadableFn = Loadable
      let loadableOptions = defaultOptions
  
      if (typeof dynamicOptions.then === 'function') {
          // Support for direct import(),
          // eg: dynamic(import('../hello-world'))
          loadableOptions.loader = () => dynamicOptions
      } else if (typeof dynamicOptions === 'object') {
          // Support for having first argument being options,
          // eg: dynamic({loader: import('../hello-world')})
          loadableOptions = { ...loadableOptions, ...dynamicOptions }
      }
  
      // Support for passing options,
      // eg: dynamic(import('../hello-world'), {loading: () => <p>Loading something</p>})
      loadableOptions = { ...loadableOptions, ...options }
  
      // Support for `render` when using a mapping,
      // eg: `dynamic({ modules: () => {return {HelloWorld: import('../hello-world')}, render(props, loaded) {} } })
      if (dynamicOptions.render) {
          loadableOptions.render = (loaded, props) =>
          dynamicOptions.render(props, loaded)
      }
  
      // Support for `modules` when using a mapping,
      // eg: `dynamic({ modules: () => {return {HelloWorld: import('../hello-world')}, render(props, loaded) {} } })
      if (dynamicOptions.modules) {
          loadableFn = Loadable.Map
          const loadModules = {}
          const modules = dynamicOptions.modules()
          Object.keys(modules).forEach(key => {
              const value = modules[key]
              if (typeof value.then === 'function') {
                  loadModules[key] = () => value.then(mod => mod.default || mod)
                  return
              }
              loadModules[key] = value
          })
          loadableOptions.loader = loadModules
      }
  
      return loadableFn(loadableOptions)
  }
docs: Thanks to umi