Mehmet Yatkı yatki

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'typeof import(".../src/formats")'.
  No index signature with a parameter of type 'string' was found on type 'typeof import(".../src/formats")'

import * as formats from './formats';
 
for (const formatName of Object.keys(formats)) {

Gettings started writing a ESLint rule

First, take a look at the ESLint rule documentation. Just skim it for now. It's very long and boring. You can come back to it later.

ESLint rules works on the AST (Abstract Syntax Tree) representation of the code. In short, this is a tree structure that describes the code in a very verbose form. ESLint walks this tree and rules can subscribe to be notified when it hits a specific node type, like a Literal type, which could be the "hello" part of const welcome = "hello";.

Go ahead and play around with some code in AST Explorer (Make sure the parser is espree). It's a great tool!

Here are some good articles on the subject (ignore the scaffolding parts):

https://insideops.wordpress.com/2015/12/08/creating-custom-rules-for-eslint/

	{
	"plugins": [
	"spellcheck"
	],
	"rules":
	// Spellcheck
	//
	"spellcheck/spell-checker": ["warn", {
	"skipWords": [
	// own names

	const promisifyOnce = (emitter, event, reject = false) => new Promise((resolve, reject) => {
	emitter.once(event, (...data) => {
	if (reject) {
	return reject(...data);
	}
	return resolve(...data);
	});
	});

	// Usage:

	const x = [
	new Promise(resolve => setTimeout(() => resolve('500'), 500)),
	new Promise(resolve => setTimeout(() => resolve('600'), 600)),
	new Promise(resolve => setTimeout(() => resolve('100'), 100)),
	]

	for await (let o of x) {
	console.log(o);
	}