# consistent-return

> Require every `return` in a function to have a value, or none of them

A function that returns a value on one path and nothing on another sometimes gives its caller `undefined`. That can be on purpose, but often someone forgot a value, or the function runs off the end by accident.

The function's first `return` sets the expectation. Every `return` that differs from it is reported, and so is a function that returns a value but can also run off the end.

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. To turn it on:

```toml bunfig.toml
[lint.rules]
"consistent-return" = "error" # or "warn"
```

Every option, set to its default:

```toml bunfig.toml
[lint.rules]
"consistent-return" = ["error", {
  treatUndefinedAsUnspecified = false,
}]
```

{/* End of the generated section. */}

## Examples

Reported:

{/* bad */}
```js
function findUser(id) {
  if (!id) {
    return;
  }
  return users.get(id);
}
```

{/* bad */}
```js
function discount(order) {
  if (order.total > 100) {
    return 10;
  }
}
```

Not reported:

{/* good */}
```js
function findUser(id) {
  if (!id) {
    return undefined;
  }
  return users.get(id);
}

function discount(order) {
  if (order.total > 100) {
    return 10;
  }
  return 0;
}

function log(message) {
  if (!enabled) {
    return;
  }
  console.log(message);
}
```

## Options

| Option | Default | What it does |
| --- | --- | --- |
| `treatUndefinedAsUnspecified` | `false` | Treat `return undefined;` and `return void 0;` the same as `return;`. |

{/* bad {"options": [{"treatUndefinedAsUnspecified": true}]} */}
```js
function findUser(id) {
  if (!id) {
    return undefined;
  }
  return users.get(id);
}
```

## When not to use it

In TypeScript, the compiler option `noImplicitReturns` finds the same mistakes and knows the function's return type.