# functional/no-conditional-statements 📝 Disallow conditional statements. 💼🚫 This rule is enabled in the following configs:  `noStatements`, ✅ `recommended`, 🔒 `strict`. This rule is _disabled_ in the ☑️ `lite` config. 💭 This rule requires [type information](https://typescript-eslint.io/linting/typed-linting). This rule disallows conditional statements such as `if` and `switch`. ## Rule Details Conditional statements are not a good fit for functional style programming as they are not expressions and do not return a value. Instead consider using the [ternary operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator) which is an expression that returns a value: For more background see this [blog post](https://hackernoon.com/rethinking-javascript-the-if-statement-b158a61cd6cb) and discussion in [tslint-immutable #54](https://github.com/jonaskello/tslint-immutable/issues/54). ### ❌ Incorrect ```js /* eslint functional/no-conditional-statements: "error" */ let x; if (i === 1) { x = 2; } else { x = 3; } ``` ### ✅ Correct ```js /* eslint functional/no-conditional-statements: "error" */ const x = i === 1 ? 2 : 3; ``` ```js /* eslint functional/no-conditional-statements: "error" */ function foo(x, y) { return x === y // if ? 0 : x > y // else if ? 1 : -1; // else } ``` ## Options This rule accepts an options object of the following type: ```ts type Options = { allowReturningBranches: boolean | "ifExhaustive"; ignoreCodePattern?: ReadonlyArray | string; }; ``` ### Default Options ```ts const defaults = { allowReturningBranches: false, }; ``` ### Preset Overrides #### `recommended` and `lite` ```ts const recommendedAndLiteOptions = { allowReturningBranches: true, }; ``` ### `allowReturningBranches` #### `true` Allows conditional statements but only if all defined branches end with a return statement or other terminal. This allows early escapes to be used. ```js function foo(error, data) { if (error) { return; } // ... - Do stuff with data. } ``` #### `"ifExhaustive"` This will only allow conditional statements to exist if every case is taken into account and each has a return statement or other terminal. In other words, every `if` must have an `else` and every `switch` must have a default case. This allows conditional statements to be used like [do expressions](https://github.com/tc39/proposal-do-expressions). ```js const x = (() => { switch (y) { case "a": return 1; case "b": return 2; default: return 0; } })(); ``` Note: Currently this option is not useable with the [no-else-return](https://eslint.org/docs/rules/no-else-return) rule; `else` statements must contain a return statement. ### `ignoreCodePattern` This option takes a RegExp string or an array of RegExp strings. It allows for the ability to ignore violations based on the test condition of the `if` statement. Note: This option has no effect on `switch` statements.