@studnicky/v8/memoize-array-length

Disallows assigning array.length or array["length"] to either identifier in an identifier-to-identifier for or while loop comparison inside that loop's body. The rule catches a self-defeating form such as a manually memoized bound reassigned to .length on every iteration; it does not require memoizing a length in the first place.

On Node v24, the direct i < array.length loop measured 2.327 ms and the memoized form measured 3.256 ms over 5,000,000 iterations: memoization was 1.399x slower. TurboFan hoists an invariant length read when the array is not resized, so this rule is a code-clarity constraint rather than a claim that reading .length prevents optimization.

Fixable: No · Options: No · Suggested severity: error

✗ Incorrect

let end = items.length;

for (let index = 0; index < end; index += 1) {
  end = items.length;
  process(items[index]);
}

✓ Correct

for (let index = 0; index < items.length; index += 1) {
  process(items[index]);
}

const end = items.length;

for (let index = 0; index < end; index += 1) {
  process(items[index]);
}