TypeScript is wasting my time

Types you don't care about are unknown

export default (_: unknown, inject: Function) => {
  inject('myPlugin', /* Plugin code */);
};

Use typeof type operator and ReturnType to generate the type for you.

function makeAPI(inject: Function) {
  return {
    get(key: string): object {
      /* Code code code */
      return {}; 
    },
    set(key: string, value: object): void {
      /* Code code code */
    }
  }
}

export type API = ReturnType<typeof makeAPI>;

export default (_: unknown, inject: Function) => {
  inject('myPlugin', makeAPI(inject));
};

Other than that it's just the "cost of doing business". Those interfaces had no idea that you would be adding your plugin. So now you are merging your plugin into those existing interfaces.

Also it's not duplication. There is type declaration space and variable declaration space or as I like to put it:

• type space: where TypeScript compile time types live
• value space: where JavaScript runtime values live

The makeAPI function is pure JavaScript and lives in value space. With the help typeof and ReturnType we pulled API into type space for compile time type checking. Monkey patching those interfaces happens at runtime in value space, so TypeScript can't really track where it is going to end up - yet value space code is going to try to access it in those places so it becomes necessary to tell TypeScript where it is going to show up.

const ENTITIES = ['users', 'articles'] as const;
type Entities = typeof ENTITIES[number]; // "users" | "articles"

type BuilderStep = (this: URLBuilder, id?: string) => URLBuilder;
type URLBuilder = {
  currentUser: (this: URLBuilder) => URLBuilder;
  toString: () => string;
} & Record<Entities, BuilderStep>;

function API() {
  let url = 'api';
  const builder: Partial<URLBuilder> = {
    currentUser() {
      return this.users('4321');
    },
    toString() {
      return url;
    },
  };

  ENTITIES.forEach((entity) => {
    const fn: BuilderStep = function (id) {
      const idSegment = id ? `/${id}` : '';
      url += `/${entity}${idSegment}`;
      return this;
    };

    builder[entity] = fn;
  });

  return builder as URLBuilder;
}

// Usage
console.log(`${API().users('4321').articles()}`); // => 'api/users/4321/articles'

• const assertion
• type aliases
• Mapped Types
• this parameters
• Intersection types
• Record<Keys,Type>
• Partial<Type>
• Type assertions

TypeScript is a compile time static type checker. Here you are assembling an object dynamically at runtime (in value space). TypeScript hates that - so you have to take TypeScript by the hand and explain to it like it's five.

The big help here is Partial<URLBuilder> because it makes all the members of the object optional so things can be added piece by piece. However for methods we have to assert that this will be a full blown URLBuilder by the time the method runs.

In the end you as the developer have to take the responsibility of asserting that you are sure that builder is no longer Partial but a fullblown URLBuilder.

Sorry to say but yes it's you. Typescript is a superset of js so you could just rename the files, turn down the strict mess of your linter and incrementally turn your codebase into more of a proper ts codebase.

Some of the challenges you write about can be solved with a simple Google search.

Using anonymous types really doesn't help. Your compact issue for example, and the url builder return type (which is missing, btw).

It's a little bit of time invested now, but easily recouped by preventing bugs before they occur while writing code in the future. I've upgraded a large corp application and it was a pain as well, but well worth it. Using a good ide like webstorm can take some of the tedious work out of your hands, so is highly recommendable

After working with both we ended up with a middle point solution that has become our favourite, and it's using TS + JS but not in separate files, let me explain:

You can just add TS Pragma at the top of your JS files
// @ts-check

Then declare the types you want with JSDoc

Quick example:

// @ts-check
const fs = require('fs');

/**
 * encodes a file into base64
 * @param {import('fs').PathOrFileDescriptor} file 
 * @returns {string}
 */
const base64_encode = (fileSource) => {
  /** @type {Buffer} */
  var file = fs.readFileSync(fileSource);
  return Buffer.from(file).toString('base64');
}

If something bothers you (let's add an example):

// @ts-check
const { Sequelize } = require('sequelize');

const sequelize = new Sequelize(process.env.DB_NAME, process.env.DB_USER, process.env.DB_PASSWORD, {
  host: process.env.DB_ADDR,
  dialect: process.env.DB_DIALECT,
});

It will complain about Type 'string' is not assignable to type 'Dialect'.ts(2322) in the dialect option.

Do I really need to create a Dialect for that when a string stored in a config/env file will do the exact same job?

I mean, I'm not going to suddenly use a different dialect on the DB, it will be the same always for this project and if I need to change something its just about editing the config/env file, migrate the models, migrate the current data... it's not something you do "by mistake" or whatever, you really need to invest time on it.

Moreover I'm not working with POO which means no custom classes are (nor will be) added to the project.

Quick fix:

// @ts-check
const { Sequelize } = require('sequelize');

const sequelize = new Sequelize(process.env.DB_NAME, process.env.DB_USER, process.env.DB_PASSWORD, {
  host: process.env.DB_ADDR,
  // @ts-ignore
  dialect: process.env.DB_DIALECT,
});

This way (using TS pragma + JSDoc) you will

• Get your project well documented.
• Get type checking where and when it's really meaningful and helpful.
• Works in dev time, handled by VSCode out of the box without the need of adding TS as dependency in your project or configuring anything.
• No time wasted compiling (transpiling) TS to JS.
• Faster dev times.
• No excuses for anyone not documenting the code with fallacies like "my code is good enough to be understood by anyone so it's auto-documented" or BS like that anymore. 😆
• Get type inference for your variables and functions either be in the same file or imported/required from another.
• Be happier (opinionated sentence).

It's a win-win, the best of both worlds and (to me) the way to go..

We already tried it in a big project that is in production since 5 to 6 months ago (at the time of writing that).

We had 2 webapps, one with JS another one using TS and this third one using the approach described in this comment.

Now, no one in the team wants TS anymore, that was unexpected at the beginning but we're getting faster development times, the code is much more understandable by anyone new in the project, no flaws due to types, makes PR review easier and so on.

We're thinking to migrate the TS one to this approach first while adding this approach in the JS one anytime we need to edit a file, find a bug, add a feature and so on.

Thoughts on that? Have you ever tried this approach?

I cursed a lot when I started to use typescript as well. I felt as if someone tied rocks to my hands when I was able to write perfectly working JS before.

Soon you will adapt and naturally write code that gets along easier with TS. This is not exactly a drawback. Maybe it gets less elegant here and there, but its mostly for the better, trust me. Where you are, I have been - where I am, you will be :D

I don't have time to go into every single of your examples, but at least the first two:

Object.keys(localStorage).forEach((key) => {
  store.commit('cache/init', {
    key,
    value: JSON.parse(localStorage.getItem(key)),
  });
});

TSC does a lot of code checking but it has its limits. It does not know that when you call localStorage.getItem(key), the key HAS to be present because its derived from the current keys in localStorage. To mitigate this, you can give the TSC a hint that a given value WILL be there by adding an exclamation mark: JSON.parse(localStorage.getItem(key)!)

This is somewhat the same problem:

function formatNumber(value: number, lang: string = 'en') {
  const options = {
    notation: 'compact',
    maximumFractionDigits: 1,
  };
  const formatter = Intl.NumberFormat(lang, options);
  return formatter.format(value);
}

TSC sees: "ah, he assigned a string here" and internally derives the type of "options" to {notation: string, maximumFractionDigits: number}. He is not exactly incorrect here. But string does not match the options wanted for NumberFormat. So what you need to do is:

function formatNumber(value: number, lang: string = 'en') {
  const options: {notation: "compact", maximumFractionDigits: number} = {
    notation: 'compact',
    maximumFractionDigits: 1,
  };
  const formatter = Intl.NumberFormat(lang, options);
  return formatter.format(value);
}

Having to convert a project is always a headache no matter what it is to what it will be. I have been recommending to customers to make a new major version and port to typescript scaffolding from scratch with typescript and slotting in the core bits to suit.

I haven't used Nuxt, but the first two can be simply done as follows:

• Using the string 'null' as a backup like this: Playground

• Using the exact type of what it expects: Playground or directly pass it in the function instead of declaring a new variable.

I suggest you trust your own reasoning and intuition more. TS is cool and all but it is not the silver bullet that the dogmatic part of its community makes it out to be. Most importantly it does not come without tradeoffs or costs (like everthing else). For some projects and some programmers the benefits are larger than the costs but it is not always the case. Should you learn it? By all means yes. Should you use it? When it's appropriate. Should you adopt a victim mentality and worship at its feet? No way sir.

Maybe you should ! Come suffer with me ;)

Thanks a lot for taking the time to address every points. I really want to understand why so many are enthralled by TS. Be sure that on monday, I'll be going back to this with your help.

I don't want to go into all of your issues. So I stop at the first one since no one mentioned this:

function formatNumber(value: number, lang: string = 'en') {
  const options = {
    notation: 'compact' as const,
    maximumFractionDigits: 1,
  };
  const formatter = Intl.NumberFormat(lang, options);
  return formatter.format(value);
}

Solves your problem here. By default, TS makes / types these objects loosely, as such at it sees

interface TempInterface {
  notation: string;
  maximumFractionDigits: number;
}

which makes sense as nothing prevents you to write options.notation = 'foo'. I think you fall into the trap of thinking that const means immutable, but it rather means "cannot be reassigned".

The alternative to help TypeScript here with the as const is to just tell it the right interface in the assignment.