prefer-direct-iteration.md

prefer-direct-iteration

📝 Prefer direct iteration over default iterator method calls.

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

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

Some built-ins expose their default iterator through both [Symbol.iterator]() and a named method. For example, Map#entries() is the same iterator as Map#[Symbol.iterator](), and Array#values() is the same iterator as Array#[Symbol.iterator]().

When the result is immediately consumed as an iterable, the named method is redundant.

This rule reports:

• .entries() for Map, FormData, and URLSearchParams
• .values() for Array, typed arrays, and Set
• .keys() for Set

It intentionally does not report unknown receivers, or methods that are not equivalent to the default iterator, such as Array#entries(), Map#values(), or Set#entries().

With TypeScript type information, this rule can also recognize supported built-ins through type aliases and inferred references. Without type information, it only uses direct syntax and simple annotations.

Examples

// ❌
const map = new Map();
for (const entry of map.entries()) {}

// ✅
const map = new Map();
for (const entry of map) {}

// ❌
const array = [1, 2, 3];
const values = [...array.values()];

// ✅
const array = [1, 2, 3];
const values = [...array];

// ❌
const map = new Map();
const copy = new Map(map.entries());

// ✅
const map = new Map();
const copy = new Map(map);

// ✅ — `Array#entries()` yields `[index, value]` pairs, while arrays iterate values by default
for (const entry of array.entries()) {}

// ✅ — unknown receiver
for (const item of collection.values()) {}