Exports is not defined how to rewrite to custom loader for webpack 4?

Question

webpack

There is a custom webpack loader written for webpack 3. There is such code

return `
    ...
   React.createElement(exports.default)
   ...
`

Everything is good in webpack 3. In webpack 4 it says Uncaught ReferenceError: exports is not defined. What has changed in webpack 4 and how to solve the problem?