# complexity

> Enforce a maximum number of branches in a function

Every branch in a function is one more path to keep in mind and to test. This rule counts them and reports any function with more than 20.

The count starts at 1. Each of these adds 1: `if`, `? :`, a loop, a `case`, a `catch`, `&&`, `||`, `??`, their assignment forms such as `||=`, `?.`, and a default value for a parameter or in destructuring. Nested functions are counted separately. Class field initializers and static blocks are counted too.

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

Every option, set to its default. The ones that are commented out are unset by default.

```toml bunfig.toml
[lint.rules]
"complexity" = ["error", {
  max = 20,
  variant = "classic", # "classic" or "modified"
  # maximum = <number>,
}]
```

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

## Examples

With a maximum of 3, this function is reported. It has a complexity of 4:

{/* bad {"options": [3]} */}
```js
function shipping(order) {
  if (order.total > 100) {
    return 0;
  } else if (order.express) {
    return 15;
  } else if (order.country !== "US") {
    return 25;
  }
  return 5;
}
```

Not reported:

{/* good {"options": [3]} */}
```js
function shipping(order) {
  if (order.total > 100) {
    return 0;
  }
  return order.express ? 15 : standardRate(order.country);
}

function standardRate(country) {
  return country === "US" ? 5 : 25;
}
```

## Options

```toml bunfig.toml
[lint.rules]
complexity = ["error", 10]
```

The option is either a number (the maximum) or an object:

| Option | Default | What it does |
| --- | --- | --- |
| `max` | `20` | The highest complexity allowed. `maximum` is an older name for it. |
| `variant` | `"classic"` | `"modified"` counts a whole `switch` as 1, no matter how many `case`s it has. |

Three `case`s give this function a complexity of 4. `default` doesn't count:

{/* bad {"options": [{"max": 3}]} */}
```js
function label(status) {
  switch (status) {
    case "open":
      return "Open";
    case "merged":
      return "Merged";
    case "closed":
      return "Closed";
    default:
      return "Unknown";
  }
}
```

With `"modified"`, the same function has a complexity of 2:

{/* good {"options": [{"max": 2, "variant": "modified"}]} */}
```js
function label(status) {
  switch (status) {
    case "open":
      return "Open";
    case "merged":
      return "Merged";
    case "closed":
      return "Closed";
    default:
      return "Unknown";
  }
}
```