Rule proposal: no inline callbacks before other parameters

[fregante]

Description

Initially reported in sindresorhus/memoize#97, it's bad practice to place arguments after functions because functions tend to be inlined and eclipse the parameters that follow them.

This could actually be two rules:

• don't allow calling foo(() => {}, {something: true})
• don't allow declaring function foo(cb, options) {}

@sindresorhus doesn't like the latter so I'll focus on the first part 😅

Fail

element.addEventListener('click', () => {
	// long
}, {once: true})

const memoized = memoize(() => {
	// long
}, {
	cache: new WeakMap(),
})

Pass

element.addEventListener('click', () => {
	// long
}) // No follow-up argument

const memoized = memoize(() => {
	// long
}) // No follow-up argument

const handler = () => {
	// long
};
element.addEventListener('click', handler, {once: true})

const raw = () => {
	// long
};
const memoized = memoize(raw, {
	cache: new WeakMap(),
})

{maxStatements: 3}

element.addEventListener('click', () => short(), {once: true})

const memoized = memoize((x) => alert(x), {
	cache: new WeakMap(),
})

Additional info

This might conflict with https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/no-array-callback-reference.md in some cases (reduce) if maxStatements defaults to 0

const foo = array.reduce(callback, 0);
// ❌ no-array-callback-reference

👇

const foo = array.reduce((a, b) => a + b, 0);
// ❌ no-inline-function-sometimes

[sindresorhus]

How about allowing one-line functions?

[fregante]

What about

mem(async url => {
  const r = await fetch(url);
  return r.json();
}, {
  something
};

For the purpose of this rule, this still seems readable. That's why it should probably default to "3 statements" and warn that "the inline function is too long and impacts readability" for anything longer.