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Optimizations

Aside from just bundling your module into different formats, TSDX comes with some optimizations for your convenience. They yield objectively better code and smaller bundle sizes.

After TSDX compiles your code with TypeScript, it processes your code with 3 Babel plugins:

Development-only Expressions + Treeshaking

babel-plugin-annotate-pure-calls + babel-plugin-dev-expressions work together to fully eliminate dead code (aka treeshake) development checks from your production code. Let's look at an example to see how it works.

Imagine our source code is just this:

// ./src/index.ts
export const sum = (a: number, b: number) => {
  if (process.env.NODE_ENV !== 'production') {
    console.log('Helpful dev-only error message');
  }
  return a + b;
};

tsdx build will output an ES module file and 3 CommonJS files (dev, prod, and an entry file). If you want to specify a UMD build, you can do that as well. For brevity, let's examine the CommonJS output (comments added for emphasis):

// Entry File
// ./dist/index.js
'use strict';
// This determines which build to use based on the `NODE_ENV` of your end user.
if (process.env.NODE_ENV === 'production') {
  module.exports = require('./mylib.cjs.production.js');
} else {
  module.exports = require('./mylib.development.cjs');
}
// CommonJS Development Build
// ./dist/mylib.development.cjs
'use strict';
const sum = (a, b) => {
  {
    console.log('Helpful dev-only error message');
  }
  return a + b;
};
exports.sum = sum;
//# sourceMappingURL=mylib.development.cjs.map
// CommonJS Production Build
// ./dist/mylib.cjs.production.js
'use strict';
exports.sum = (s, t) => s + t;
//# sourceMappingURL=test-react-tsdx.cjs.production.js.map

AS you can see, TSDX stripped out the development check from the production code. This allows you to safely add development-only behavior (like more useful error messages) without any production bundle size impact.

For ESM build, it's up to end-user to build environment specific build with NODE_ENV replace (done by Webpack 4 automatically).

Rollup Treeshaking

TSDX's rollup config removes getters and setters on objects so that property access has no side effects. Don't do it.

Advanced babel-plugin-dev-expressions

TSDX will use babel-plugin-dev-expressions to make the following replacements before treeshaking.

__DEV__

Replaces

if (__DEV__) {
  console.log('foo');
}

with

if (process.env.NODE_ENV !== 'production') {
  console.log('foo');
}

IMPORTANT: To use __DEV__ in TypeScript, you need to add declare var __DEV__: boolean somewhere in your project's type path (e.g. ./types/index.d.ts).

// ./types/index.d.ts
declare var __DEV__: boolean;

Note: The dev-expression transform does not run when NODE_ENV is test. As such, if you use __DEV__, you will need to define it as a global constant in your test environment.

invariant

Replaces

invariant(condition, 'error message here');

with

if (!condition) {
  if ('production' !== process.env.NODE_ENV) {
    invariant(false, 'error message here');
  } else {
    invariant(false);
  }
}

Note: TSDX doesn't supply an invariant function for you, you need to import one yourself. We recommend https://github.com/alexreardon/tiny-invariant.

To extract and minify invariant error codes in production into a static codes.json file, specify the --extractErrors flag in command line. For more details see Error extraction docs.

warning

Replaces

warning(condition, 'dev warning here');

with

if ('production' !== process.env.NODE_ENV) {
  warning(condition, 'dev warning here');
}

Note: TSDX doesn't supply a warning function for you, you need to import one yourself. We recommend https://github.com/alexreardon/tiny-warning.

Using lodash

If you want to use a lodash function in your package, TSDX will help you do it the right way so that your library does not get fat shamed on Twitter. However, before you continue, seriously consider rolling whatever function you are about to use on your own. Anyways, here is how to do it right.

First, install lodash and lodash-es as dependencies

yarn add lodash lodash-es

Now install @types/lodash to your development dependencies.

yarn add @types/lodash --dev

Import your lodash method however you want, TSDX will optimize it like so.

// ./src/index.ts
import kebabCase from 'lodash/kebabCase';
export const KebabLogger = (msg: string) => {
  console.log(kebabCase(msg));
};

For brevity let's look at the ES module output.

import o from"lodash-es/kebabCase";const e=e=>{console.log(o(e))};export{e as KebabLogger};
//# sourceMappingURL=test-react-tsdx.esm.production.js.map

TSDX will rewrite your import kebabCase from 'lodash/kebabCase' to import o from 'lodash-es/kebabCase'. This allows your library to be treeshakable to end consumers while allowing to you to use @types/lodash for free.

Note: TSDX will also transform destructured imports. For example, import { kebabCase } from 'lodash' would have also been transformed to `import o from "lodash-es/kebabCase".

Error extraction

After running --extractErrors, you will have a ./errors/codes.json file with all your extracted invariant error codes. This process scans your production code and swaps out your invariant error message strings for a corresponding error code (just like React!). This extraction only works if your error checking/warning is done by a function called invariant.

Note: We don't provide this function for you, it is up to you how you want it to behave. For example, you can use either tiny-invariant or tiny-warning, but you must then import the module as a variable called invariant and it should have the same type signature.

⚠️Don't forget: you will need to host the decoder somewhere. Once you have a URL, look at ./errors/ErrorProd.js and replace the reactjs.org URL with yours.

Known issue: our transformErrorMessages babel plugin currently doesn't have sourcemap support, so you will see "Sourcemap is likely to be incorrect" warnings. We would love your help on this.

TODO: Simple guide to host error codes to be completed