How To Make Dynamic Import/require Depend Of Variable With Code Cleanup?

I have react app created by "react-create-app" with latest react 16.12 and Webpack

I need to make import with dependence on variable, like it:

    if (process.env.SOMEVAR === "a1") Routes = require("./xxx").default;
    if (process.env.SOMEVAR === "a2") Routes = require("./yyy").default;
    if (process.env.SOMEVAR === "a3") Routes = require("./zzz").default;

Run command: set "SOMEVAR=a1" && npm run build

This code will make main.chunk.js with this 3 modules xxx/yyy/zzz inside, without dependency of SOMEVAR

I've accidentally discovered that when I use NODE_ENV variable name - it works like I need! Example:

    if (process.env.NODE_ENV === "production") Routes = require("./xxx").default;
    if (process.env.NODE_ENV === "development") Routes = require("./yyy").default;
    if (process.env.NODE_ENV === "test") Routes = require("./zzz").default;

Run command: set "NODE_ENV=production" && npm run build

This code will make main.chunk.jswith only xxx module inside!

Question: How to make any other variables with same effect instead of NODE_ENV (I need to have inside of build only modules which uses after my if)? How it works? I cant find any info about this effect in "WebPack docs".

From the provided example i think this is not the best approach.

You can define a dynamic pluggin in that exposes a custom global variable to the build. Adding to your webpack plugins config something like :

new webpack.DefinePlugin({
    EnabledRoutes: {
        testing: true,
        production: true,
        development: true
    }
})

And this way you can use process environment or reading a build config like this:

new webpack.DefinePlugin({
    EnabledRoutes: {
        testing: process.env.ROUTES_TESTING,
        production: Config.routes.production,
        development: true
    }
})

And in the client router directly you can check to add the additional routes:

if(EnabledRoutes.testing)
{
    APPEND routes.
}

or

if (EnabledRoutes.testing) Routes = require("./xxx").default;