@total-typescript/ts-reset

ts-reset

ts-reset acts like a CSS reset for TypeScript. It improves typings for JavaScript API's like fetch, JSON.parse and .filter(), making them safer and smarter.

// Import in a single file, then across your whole project...
import "@total-typescript/ts-reset";

// .filter just got smarter!
const filteredArray = [1, 2, undefined].filter(Boolean); // number[]

// Get rid of the any's in JSON.parse and fetch
const result = JSON.parse("{}"); // unknown

fetch("/")
  .then((res) => res.json())
  .then((json) => {
    console.log(json); // unknown
  });

Get Started

1. Install: npm i @total-typescript/ts-reset

2. Import once into any .ts or .tsx file:

import "@total-typescript/ts-reset";

1. Enjoy improved typings across your entire project.

Installing only certain rules

By importing from @total-typescript/ts-reset, you're bundling all the recommended rules.

To only import the rules you want, you can import like so:

// Makes JSON.parse return unknown
import "@total-typescript/ts-reset/json-parse";

// Makes await fetch().then(res => res.json()) return unknown
import "@total-typescript/ts-reset/fetch";

Below is a full list of all the rules available.

Caveats

Use ts-reset in applications, not libraries

ts-reset is designed to be used in application code, not library code. Each rule you include will make changes to the global scope. That means that, simply by importing your library, your user will be unknowingly opting in to ts-reset.

Rules

Make JSON.parse return unknown

import "@total-typescript/ts-reset/json-parse";

JSON.parse returning any can cause nasty, subtle bugs. Frankly, any any's can cause bugs because they disable typechecking on the values they describe.

// BEFORE
const result = JSON.parse("{}"); // any

By changing the result of JSON.parse to unknown, we're now forced to either validate the unknown to ensure it's the correct type (perhaps using zod), or cast it with as.

// AFTER
import "@total-typescript/ts-reset/json-parse";

const result = JSON.parse("{}"); // unknown

Make .json() return unknown

import "@total-typescript/ts-reset/fetch";

Just like JSON.parse, .json() returning any introduces unwanted any's into your application code.

// BEFORE
fetch("/")
  .then((res) => res.json())
  .then((json) => {
    console.log(json); // any
  });

By forcing res.json to return unknown, we're encouraged to distrust its results, making us more likely to validate the results of fetch.

// AFTER
import "@total-typescript/ts-reset/fetch";

fetch("/")
  .then((res) => res.json())
  .then((json) => {
    console.log(json); // unknown
  });

Make .filter(Boolean) filter out falsy values

import "@total-typescript/ts-reset/filter-boolean";

The default behaviour of .filter can feel pretty frustrating. Given the code below:

// BEFORE
const filteredArray = [1, 2, undefined].filter(Boolean); // (number | undefined)[]

It feels natural that TypeScript should understand that you've filtered out the undefined from filteredArray. You can make this work, but you need to mark it as a type predicate:

const filteredArray = [1, 2, undefined].filter((item): item is number => {
  return !!item;
}); // number[]

Using .filter(Boolean) is a really common shorthand for this. So, this rule makes it so .filter(Boolean) acts like a type predicate on the array passed in, removing any falsy values from the array member.

// AFTER
import "@total-typescript/ts-reset/filter-boolean";

const filteredArray = [1, 2, undefined].filter(Boolean); // number[]

Make .includes on as const arrays less strict

import "@total-typescript/ts-reset/array-includes";

This rule improves on TypeScript's default .includes behaviour. Without this rule enabled, the argument passed to .includes MUST be a member of the array it's being tested against.

// BEFORE
const users = ["matt", "sofia", "waqas"] as const;

// Argument of type '"bryan"' is not assignable to
// parameter of type '"matt" | "sofia" | "waqas"'.
users.includes("bryan");

This can often feel extremely awkward. But with the rule enabled, .includes now takes a widened version of the literals in the const array.

// AFTER
import "@total-typescript/ts-reset/array-includes";

const users = ["matt", "sofia", "waqas"] as const;

// .includes now takes a string as the first parameter
users.includes("bryan");

This means you can test non-members of the array safely.

It also makes .includes a type predicate, meaning you can use it to narrow wider types to a set enum:

import "@total-typescript/ts-reset/array-includes";

const users = ["matt", "sofia", "waqas"] as const;

const isUser = (input: string) => {
  if (users.includes(input)) {
    // input is narrowed to "matt" | "sofia" | "waqas"
    console.log(input);
  }
};

Removing any[] from Array.isArray()

import "@total-typescript/ts-reset/is-array";

When you're using Array.isArray, you can introduce subtle any's into your app's code.

// BEFORE

const validate = (input: unknown) => {
  if (Array.isArray(input)) {
    console.log(input); // any[]
  }
};

With is-array enabled, this check will now mark the value as unknown[]:

// AFTER
import "@total-typescript/ts-reset/is-array";

const validate = (input: unknown) => {
  if (Array.isArray(input)) {
    console.log(input); // unknown[]
  }
};

Changelog

0.2.0

Minor Changes

• e5a33c9: Added support for array.includes

Patch Changes

• 8fe8e29: Improved filter-boolean to handle falsy values, not just NonNullable values