Things typescript didn't catch that should probably be lint rules

2023-02-05

This is a short list of silly things that I wish Typescript would have caught for me, but are silly logic errors

#Using Object.entries accidentally instead of Object.fromEntries

Typescript will not complain if you use Object.entries instead of Object.fromEntries

const stuff = [1, 2, 3]
 
// woops, meant to use Object.fromEntries
Object.entries(stuff.map(entry => [entry, { id: entry }]))

playground

Summary: should probably be a lint rule (a "types required" lint rule, a la @typescript-eslint) not to accept arrays for Object.entries

Update 02-27-23: Proposing this rule here https://github.com/typescript-eslint/typescript-eslint/issues/6537

#Passing garbage to the second argument of Array.prototype.map accidentally

function doStuff(arr: number[], extra?: { sayHiToMom: boolean }) {
  if (extra?.sayHiToMom) {
    console.log('Hi mom')
  }
  return arr
}
 
const stuff = [1, 2, 3]
 
// woops, meant to pass that as second argument to doStuff
doStuff(stuff.map(a => a * 2, { sayHiToMom: true }))

playground

This one would be difficult for typescript to catch, the second arg is "thisArg", what the callback refers to as this

Summary: should probably be a lint rule to avoid this second arg, as it is obscure

Update 02-27-23: This lint rule exists already :) https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/no-array-method-this-argument.md#disallow-using-the-this-argument-in-array-methods

#Any others?

Any other ones that you find in your work? This is just from the past week for me :)

I will need to learn how to make eslint rules!