There are probably couple of ways to handle conditional compilation, but one I know it works is to use dynamic imports

// Just to not throw an exception in the snippet
const process = {
 env:{
   USE_AXIOS: false
 }
}
// ------------------------------------------------






// Solution
if (process.env.USE_AXIOS) {
  import('axios').then(({default: axios}) => {
    if ('get' in axios) {
      console.log('axios in use');
    }
  });
}

full code example is here webpack-conditional-complation

you can examine a produced code

• here is an axios bundled in separated file
• here is a compiled ./src/include-axios-base-on-env.js to with-axios.js with flag USE_AXIOS=true
• here is a compiled ./src/include-axios-base-on-env.js to without-axios.js with flag USE_AXIOS=false