Cannot find documentation for metro.config.js > resolver > resolveRequest

I cannot find any docs for the resolveRequest function listed at https://facebook.github.io/metro/docs/configuration#resolverequest

I implemented the function and inspected it with console.log(arguments), but when I return a string, it throws a type error.

resolveRequest(context, module, platform){
      let res = require.resolve(path.resolve(context.originModulePath, module));
      console.log(res);
      return res;
}

[robhogan]

Ah I see - if you init a new React Native app today you’ll get react-native@0.67.2 (latest stable) which includes metro@0.66.2, so the metro docs prior to 0.68 apply. Unfortunately, we don’t yet have a versioned docs website for metro, but you can access the raw docs at that point from github - https://github.com/facebook/metro/tree/v0.66.2/docs.

Prior to metro 0.68, context.resolveRequest points directly back to your own custom resolver, rather than the default resolver - so calling it from your own resolver creates a recursive loop which eventually throws, gets caught internally and manifests as a failed resolution. To access the default resolver you do need to use metro-resolver and ensure that you unset resolveRequest when passing the context, so the last thing you try is almost correct. The critical difference is that, in <0.68, the resolver takes a fourth argument, “realModuleName”.

So in summary, these are equivalent:

For Metro >=0.68

// metro.config.js

module.exports = {
  resolver: {
    resolveRequest: (context, moduleName, platform) => {
      // For example: redirecting `require('path')` to your own mock
      if (moduleName === 'path') {
        return {
          filePath: __dirname + '/my-mock-path.js',
          type: 'sourceFile',
        };
      }
      
      // Forward everything else to the default resolver
      return context.resolveRequest(
        context,
        moduleName,
        platform,
      );
    },
  },
};

For Metro < 0.68

// metro.config.js

const defaultResolver = require('metro-resolver').resolve;

module.exports = {
  resolver: {
    resolveRequest: (context, moduleName, platform, realModuleName) => {
      // For example: redirecting `require('path')` to your own mock
      if (moduleName === 'path') {
        return {
          filePath: __dirname + '/my-mock-path.js',
          type: 'sourceFile',
        };
      }

      // Forward everything else to the default resolver
      return defaultResolver(
        {
          ...context,
          resolveRequest: null,
        },
        moduleName,
        platform,
        realModuleName,
      );
    },
  },
};

Hope that helps, and sorry for the docs confusion.

[Niryo]

There isn’t any useful docs for how to use the resolveRequest prop for module aliasing, so I played around with it and this is what I came up with:

    resolveRequest: (context, realModuleName, platform, moduleName) => {
      let module = realModuleName;
        if(realModuleName.includes('bla') || moduleName.includes('bla')) {
          module = module.replace('bla', 'blamos');
        }
        const { resolveRequest: removed, ...restContext } = context;
        return require("metro-resolver").resolve(restContext, module, platform);
    },