# yoda

> Require or disallow comparisons with the literal on the left

A "Yoda condition" puts the literal first: `"red" === color` instead of `color === "red"`. Most people read the second form more easily, because it matches how you say it: "if the color is red".

The rule checks `==`, `===`, `!=`, `!==`, `<`, `>`, `<=` and `>=` where exactly one side is a literal. Negative numbers and template literals without `${}` count as literals.

`--fix` swaps the two sides and flips the operator where needed, so `0 < count` becomes `count > 0`.

{/* 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]
"yoda" = "error" # or "warn"
```

Every option, set to its default:

```toml bunfig.toml
[lint.rules]
"yoda" = [
  "error",
  "never", # "always" or "never"
  {
    exceptRange = false,
    onlyEquality = false,
  },
]
```

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

## Examples

Reported:

{/* bad {"count": 2} */}
```js
if ("red" === color) {
  stop();
}

if (0 < count) {
  render();
}
```

Not reported:

{/* good */}
```js
if (color === "red") {
  stop();
}

if (count > 0) {
  render();
}
```

## Options

```toml bunfig.toml
[lint.rules]
yoda = ["error", "never", { exceptRange = true }]
```

The first option is `"never"` (default), which wants the literal on the right, or `"always"`, which wants it on the left. The second is an object:

| Option | Default | What it does |
| --- | --- | --- |
| `exceptRange` | `false` | Allow a range test in parentheses, such as `(0 <= x && x < 10)`. |
| `onlyEquality` | `false` | Only check `==` and `===`. |

With `exceptRange`, the value can sit between its two limits, or outside them:

{/* good {"options": ["never", {"exceptRange": true}]} */}
```js
if (0 <= index && index < items.length) {
  select(index);
}

if (value < 0 || 100 < value) {
  reject(value);
}
```

The parentheses of an `if`, a `while` or a call count. Without any around the test, it's still reported:

{/* bad {"options": ["never", {"exceptRange": true}]} */}
```js
const isPercent = 0 <= value && value <= 100;
```

With `onlyEquality`, this isn't reported:

{/* good {"options": ["never", {"onlyEquality": true}]} */}
```js
if (0 < count) {
  render();
}
```