Remove some code lines in production distribution files?

webpack-strip-block is a good solution. It removes a block of code in your production code when compiling.

/* develblock:start */
/* develblock:end */

Not limited to asserts and no redundant code in prod.

It appears the other answers are outdated. With webpack 4, you can set mode: 'production' in your webpack config.

In your code, check for development mode like this:

if (process.env.NODE_ENV === 'development') {
    if(info instanceof LogModel)
        throw new Error("not a instance of LogModel");
}

When webpack creates a bundle with mode: 'production', all the code inside these if clauses, along with the if clauses themselves, will be automatically removed from the bundle.

There is no need to use the define plugin explicitly (it is used by webpack “under the hood”), and it's not necessary to use something like webpack-unassert-loader or webpack-strip-block mentioned in other answers.

Check out this little demo repo I have made to try this out: https://github.com/pahund/webpack-devprod-experiment

A cleaner option will be using define-plugin from webpack.

In config file:

new webpack.DefinePlugin({ __DEV: JSON.stringify(true) })

app.js:

if(__DEV){ console.log("logged only in dev env") }

value of __DEV will be provided by webpack at compile time.