montype

Purpose

MonType converts your mongoose schemas into TypeScript interfaces so you don't have to.

Usage

Define your schema, like you always do; example from mongoosejs.com

const schema = new Schema({
  name:    String,
  binary:  Buffer,
  living:  Boolean,
  updated: { type: Date, default: Date.now },
  age:     { type: Number, min: 18, max: 65 },
  mixed:   Schema.Types.Mixed,
  _someId: Schema.Types.ObjectId,
  decimal: Schema.Types.Decimal128,
  array: [],
  ofString: [String],
  ofNumber: [Number],
  ofDates: [Date],
  ofBuffer: [Buffer],
  ofBoolean: [Boolean],
  ofMixed: [Schema.Types.Mixed],
  ofObjectId: [Schema.Types.ObjectId],
  ofArrays: [[]],
  ofArrayOfNumbers: [[Number]],
  nested: {
    stuff: { type: String, lowercase: true, trim: true }
  },
  map: Map,
  mapOfString: {
    type: Map,
    of: String
  }
});

Run montype --from schema.ts, and MonType will convert it into a TypeScript interface:

import mongoose from 'mongoose';

interface schema {
  name: string;
  binary: mongoose.Schema.Types.Buffer;
  living: boolean;
  updated: Date;
  age: number;
  mixed: mongoose.Schema.Types.Mixed;
  _someId: mongoose.Schema.Types.ObjectId;
  decimal: mongoose.Schema.Types.Decimal128;
  array: never[];
  ofString: string[];
  ofNumber: number[];
  ofDates: Date[];
  ofBuffer: mongoose.Schema.Types.Buffer[];
  ofBoolean: boolean[];
  ofMixed: mongoose.Schema.Types.Mixed[];
  ofObjectId: mongoose.Schema.Types.ObjectId[];
  ofArrays: never[][];
  ofArrayOfNumbers: number[][];
  nested: {
    stuff: string;
  };
  map: mongoose.Schema.Types.Map;
  mapOfString: Map<string, String>;
};

Just like that!

How it works

MonType parses the source file, and generates an AST from it. It then generates a TypeScript interface from the AST. What this means is that MonType only sees your schemas as a structured chunk of text -- nothing less, nothing more.

It's completely independent from your source, does not add additional dependencies to your project, and is highly portable and capable on working on any file that looks like a Mongoose schema.

Installation

You can install MonType by either:

• Using npx: npx montype
• Downloading a precompiled binary from the releases page
• Downloading a build artifact from a Github Actions run
• Compiling it yourself using build.sh

Configuration

MonType works by 'mapping' descriptors to their TypeScript types, for example String -> string, Number -> number, and so on.

This means that if you use a custom type in your Schema, MonType will fail:

- [×| Category.ts
-   | couldn't map the schema type 'MyType' to a TypeScript type!

To get around this, you can create a configuration file called montype.ini (or use the -c flag to provide a path) with the contents:

[types]
MyType = number

MonType will now interpret MyType as number, and succeed.

+ [✓] saved to 'MonType.ts'

Please read montype --help for more information!

Credits

Thanks to @MKRhere for listening to and answering my barrage of questions!