no-useless-spread

📝 Disallow unnecessary spread.

💼 This rule is enabled in the following configs: ✅ recommended, ☑️ unopinionated.

🔧 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.

Examples

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

// ✅
const array = [firstElement, secondElement, thirdElement];

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

// ✅
const object = {firstProperty, secondProperty, thirdProperty};

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

// ✅
foo(firstArgument, secondArgument, thirdArgument);

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

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

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

// ✅
const set = new Set(iterable);

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

// ✅
const results = await Promise.all(iterable);

// ❌
for (const foo of [...set]);

// ✅
for (const foo of set);

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

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

// ✅
const array = [...foo, bar];

// ✅
const object = {...foo, bar};

// ✅
foo(foo, ...bar);

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