lhint

Learn the Hints

A utility that automatically "learns" type hints from any data.

How it works

lhint implements its own type hint shape, everyting else is just transformations between the lhint hint shape and other shapes.
An illustration because I'm bad at explaining things:

Input -> lhint -> types -> desired-output / transformation

A more concrete example

Let's say you're building an app and you're working with some external API for fetching weather information,
this API unfortunately doesn't have very good documentation.
You can then use lhint to automatically generate types, just by giving it some samples of an API endpoint:

import { hints, TypescriptTemplateTransformer } from 'lhint';

const req = await fetch('https://the-weather-api-foobar/api');
const resp = await req.json(); // let's say this is an array of some unknown objects
const typescriptTypes = TypescriptTemplateTransformer.transform(hints.auto(resp));
console.log(typescriptTypes); // A string containing the typescript types that you can copy-paste and save somewhere.

Install

npm install lhint

API Interface

Examples

Learned hints

import { hints } from 'lhint';

// The following automatically "learns" the types
const hint = hints.auto({
  firstname: 'john',
  lastname: 'doe'
})
// And this will give the same as manually doing this:
const myHint = hints.mapping({
  firstname: hints.string(),
  lastname: hints.string()
});

Transforming

These transformations are currently available:

• typescript-template (generates typescript types in the form of a string)
• json-schema (generates json-schema objects)

Example

import { hints, TypescriptTemplateTransformer } from 'lhint';

const hint = hints.auto({
  firstname: 'john',
  lastname: 'doe',
  friend: hints.optional(hints.mapping({
    name: hints.string()
  }))
});

const ts: string = TypescriptTemplateTransformer.transform(hint);
/* 
  {
    firstname: string,
    lastname: string,
    friend?: {
      name: string
    }
  }
*/

Basic hint usage

import { hints } from 'lhint';

const name = hints.string();
const age = hints.number();
const happy = hints.boolean();
const dateOfBirth = hints.date();
const userType = hints.union([hints.literal('admin'), hints.literal('developer')]);

const flags = hints.record(hints.string(), hints.boolean());

const car = hints.mapping({
  brand: hints.string(),
  color: hints.optional(hints.string()),
  price: hints.number(),
});

// "Extract" the typescript type of a hint
const myCar: UnHint<typeof car>;
/**
  This will give the following type:
  {
    brand: string,
    color?: string,
    price: number
  }
*/

CLI

Available commands:

• transform
• hint

transform

args:

• source (a stringified JSON | URL to JSON | filepath to JSON)
• format (typescript | json-schema | hint)

example

command:

lhint transform --source "https://jsonplaceholder.typicode.com/users" --format typescript

output:

Array<{
  id: number;
  name: string;
  username: string;
  email: string;
  address: {
    street: string;
    suite: string;
    city: string;
    zipcode: string;
    geo: {
      lat: string;
      lng: string
    }
  };
  phone: string;
  website: string;
  company: {
    name: string;
    catchPhrase: string;
    bs: string
  }
}>