# functional/no-loop-statements 📝 Disallow imperative loops. 💼 This rule is enabled in the following configs: ☑️ `lite`,  `noStatements`, ✅ `recommended`, 🔒 `strict`. This rule disallows for loop statements, including `for`, `for...of`, `for...in`, `while`, and `do...while`. ## Rule Details In functional programming we want everything to be an expression that returns a value. Loops in JavaScript are statements so they are not a good fit for a functional programming style. Instead consider using `map`, `reduce` or similar. For more background see this [blog post](https://hackernoon.com/rethinking-javascript-death-of-the-for-loop-c431564c84a8) and discussion in [tslint-immutable #54](https://github.com/jonaskello/tslint-immutable/issues/54). ### ❌ Incorrect ```js /* eslint functional/no-loop-statements: "error" */ const numbers = [1, 2, 3]; const double = []; for (let i = 0; i < numbers.length; i++) { double[i] = numbers[i] * 2; } ``` ```js /* eslint functional/no-loop-statements: "error" */ const numbers = [1, 2, 3]; let sum = 0; for (const number of numbers) { sum += number; } ``` ### ✅ Correct ```js /* eslint functional/no-loop-statements: "error" */ const numbers = [1, 2, 3]; const double = numbers.map((n) => n * 2); ``` ```js /* eslint functional/no-loop-statements: "error" */ const numbers = [1, 2, 3]; const sum = numbers.reduce((carry, number) => carry + number, 0); ```