Repeated Work In Loop (ARCH3072)

Key typescript.performance.repeated-work-in-loop · Severity warning · Category performance

A computation whose inputs do not depend on the loop variable yields the same result every iteration and should be hoisted out of the loop.

Incorrect

function filter(items: Item[], config: Config): Item[] {
  const result: Item[] = [];
  for (const item of items) {
    if (item.size > config.limits.max * config.factor) {
      result.push(item);
    }
  }
  return result;
}

Correct

function filter(items: Item[], config: Config): Item[] {
  const threshold = config.limits.max * config.factor;
  const result: Item[] = [];
  for (const item of items) {
    if (item.size > threshold) {
      result.push(item);
    }
  }
  return result;
}

Fix

Move computations that do not depend on the loop variable into a variable outside the loop.