a-javascript-and-typescript-documentation-generator-based-on-typescript-compiler

A documentation generator that understands ES modules and infers types. It is powered by the TypeScript compiler, which also powers the JavaScript and TypeScript IntelliSense.

This means your documented code will be picked up by IDEs (such as Visual Studio, VS Code, or Atom-IDE) to provide auto-completions the same way!

Instead of “looking for functions/variables/constants/classes declared in a file,” it looks at each public module and walks through each exported symbol. This means it understands modules that re-exports things like this:

// index.ts
import * as doc from './doc'

export { doc }
export { default as generateDocs, GenerateDocsResult } from './generateDocs'

And generates a documentation like this:

It also works with JavaScript file. In this case, TypeScript compiler reads the type annotation from JSDog tags.

/**
 * Calculates the accuracy.
 * @param {number[]} count The 3-element array containing METICULOUS judgment,
 * PRECISE judgment, and GOOD judgment, respectively.
 * @param {number} total The total amount of possible judgments that may be given.
 * @returns the accuracy number, from 0 to 1
 */
export function calculateAccuracy (count, total) {
  return (count[0] + count[1] * 0.8 + count[2] * 0.5) / total
}

Which generates a documentation like this (note: the return type is inferred by the compiler):

Inspiration

• Visual Studio’s JavaScript IntelliSense (based on TypeScript) is very smart. It is based on TypeScript’s Language Service. However, most current documentation tools don’t benefit from that smart-ness.

• Most tools don’t infer type from source code and only reads the JSDoc tags.

• Some tools requires you to specify types and documentation in a proprietary format, which is not compatible with the IntelliSense.

• The thing I found closest to what I want is TypeDoc. It does use TypeScript compiler, but processes modules by walking through the AST, instead of looking at all exported symbols of a module (e.g. using TypeScript’s getExportsOfModule()).

• Many projects has an index.js file which only re-exports things from other modules (e.g. export { createStore } from './createStore'). However, TypeDoc does not support it yet.

• I don’t want to document a file; I want to document my module’s API surface area.

  Given that I import a module, what is there for me to use?

• VS Code’s IntelliSense tries its best to understand your code and infer stuff, instead of forcing you to document everything in its own syntax. Documentation generator tools should do the same!

• The plan: Learn how TypeScript Language Service achieves that smartness, then create a documentation generator (loosely) based on that knowledge.

Process

                `ts.createProgram()`
                        |
+-------------------+   |   +--------------------+
|    Input files    | ----> | TypeScript program |
| (.js, .ts, .d.ts) |       |   (`ts.Program`)   |
+-------------------+       +--------------------+
                                | walk the modules and symbols
                                V
     +-----------------------------------------+
     | Documentation model (JSON-serializable) |
     +-----------------------------------------+
         | generate             | export
         V                      V
     +-------------------+   +---------------+
     | Web pages (.html) |   | Model (.json) |
     +-------------------+   +---------------+

• Input files are fed into TypeScript compilers, which will resolve all modules, infer types, and lots of super-cool stuff. It results in a ts.Program object.

• a-javascript-and-typescript-documentation-generator-based-on-typescript-compiler goes through the modules, and collect documentation data, into a JSON-serializable model.

• Then we can generate a web page / readme file / whatever out of it!

Usage

Warning: This is still in development, and it might not work well. Please be prepared to dive into the source code.

Installation:

yarn global add a-javascript-and-typescript-documentation-generator-based-on-typescript-compiler

Generate HTML documentation:

a-javascript-and-typescript-documentation-generator-based-on-typescript-compiler src/index.js --html docs/api

Generate JSON to stdout:

a-javascript-and-typescript-documentation-generator-based-on-typescript-compiler src/index.js --json docs/api.json

JSON model is defined at src/generator/doc.ts.

development

1. Clone this project.

2. Install the dependencies:

   yarn

3. To generate a documentation JSON:

   yarn dev:generate <inputfile.ts ...>

4. To view and develop the documentation web page:

   ./node_modules/.bin/ts-node --doc.input=<inputfile.ts>