no-useless-spread.md

Disallow unnecessary spread

✅ This rule is enabled in the recommended config.

🔧 This rule is automatically fixable by the --fix CLI option.

• Using spread syntax in the following cases is unnecessary:

  • Spread an array literal as elements of an array literal
  • Spread an array literal as arguments of a call or a new call
  • Spread an object literal as properties of an object literal
  • Use spread syntax to clone an array created inline

• The following builtins accept an iterable, so it's unnecessary to convert the iterable to an array:

  • Map constructor
  • WeakMap constructor
  • Set constructor
  • WeakSet constructor
  • TypedArray constructor
  • Array.from(…)
  • TypedArray.from(…)
  • Promise.{all,allSettled,any,race}(…)
  • Object.fromEntries(…)

• for…of loop can iterate over any iterable object not just array, so it's unnecessary to convert the iterable to an array.

• yield* can delegate to another iterable, so it's unnecessary to convert the iterable to an array.

Fail

const array = [firstElement, ...[secondElement], thirdElement];

const object = {firstProperty, ...{secondProperty}, thirdProperty};

foo(firstArgument, ...[secondArgument], thirdArgument);

const object = new Foo(firstArgument, ...[secondArgument], thirdArgument);

const set = new Set([...iterable]);

const results = await Promise.all([...iterable]);

for (const foo of [...set]);

function * foo() {
	yield * [...anotherGenerator()];
}

function foo(bar) {
	return [
		...bar.map(x => x * 2),
	];
}

Pass

const array = [firstElement, secondElement, thirdElement];

const object = {firstProperty, secondProperty, thirdProperty};

foo(firstArgument, secondArgument, thirdArgument);

const object = new Foo(firstArgument, secondArgument, thirdArgument);

const array = [...foo, bar];

const object = {...foo, bar};

foo(foo, ...bar);

const object = new Foo(...foo, bar);

const set = new Set(iterable);

const results = await Promise.all(iterable);

for (const foo of set);

function * foo() {
	yield * anotherGenerator();
}

function foo(bar) {
	return bar.map(x => x * 2);
}