useLoader is an Isomorphic API, usually used to make asynchronous requests. During Server-Side Rendering (SSR), the server uses useLoader to prefetch the data, which is then reused on the client side.


The useLoader API is currently not supported when using Rspack as the bundler.


import { useLoader } from '@modern-js/runtime';

Function Signature

type LoaderFn = (context: runtimeContext) => Promise<unknow>;
type Options = {
  onSuccess: (data: Record<string, any>) => void;
  onError: (error: Error) => void;
  initialData: Record<string, any>;
  skip: boolean;
  params: Record<string, any>;
  static: boolean;
type ReturnData = {
  data: Record<string, any>;
  loading: boolean;
  error: Error;
  reload: (params?: Record<string, any>) => Promise<any> | undefined;
  reloading: boolean;

function useLoader(loaderFn: LoaderFn, options: Options): ReturnData;

runtimeContext can refer to useRuntimeContext.


  • loaderFn: function for loading data, returning a Promise.
  • options: optional configuration.
    • onSuccess: successful callback.
    • onError: error callback.
    • initialData: the initial data before the first execution,.
    • skip: when the value is true, the function does not execute.
    • params: when the result of the params serialization changes, the function is re-executed. params is also passed in as the second argument of the function.
    • static: when the value is true, useLoader is used for SSG.

Return Value

  • data: return data on successful execution.
  • loading: indicates whether the function is in execution.
  • error: error message when function execution fails.
  • reload: the function can be re-executed after the call.
    • params: when the value is undefined, the last value will be reused; otherwise, the function will be re-executed with the new value.
  • reloading: during the execution of the call to reload, the value of reloading is true.


function Container() {
  const { data, error, loading } = useLoader(
    async (context, params) => {
      console.log(params) // nicole
      return fetch(user);
      onSuccess: data => {
        console.log('I did success:(',  data);
      onError: error => {
        console.log('I met error:)',  error);
      initialData: { name: 'nicole', gender: 'female' },
      params: 'nicole'

  return ...;