unicorn/no-useless-spread Correctness

✅ This rule is turned on by default.

⚠️🛠️️ A dangerous auto-fix is available for this rule.

What it does

Disallows using spread syntax in following, unnecessary cases:

• 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

Why is this bad?

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(…)

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

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

Examples

Examples of incorrect code for this rule:

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

await Promise.all([...iterable]);

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

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

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

Examples of correct code for this rule:

const array = [firstElement, secondElement, thirdElement];

await Promise.all(iterable);

for (const foo of set);

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

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

How to use

To enable this rule in the CLI or using the config file, you can use:

CLI

oxlint --deny unicorn/no-useless-spread

Config (.oxlintrc.json)

{
  "rules": {
    "unicorn/no-useless-spread": "error"
  }
}

References

• Rule Source