# JavaScript

JavaScript support is available natively in Zed.

- Tree Sitter: [tree-sitter/tree-sitter-javascript](https://github.com/tree-sitter/tree-sitter-javascript)
- Language Server: [typescript-language-server/typescript-language-server](https://github.com/typescript-language-server/typescript-language-server)

## Code formatting

Formatting on save is enabled by default for JavaScript, using TypeScript's built-in code formatting. But many JavaScript projects use other command-line code-formatting tools, such as [Prettier](https://prettier.io/). You can use one of these tools by specifying an _external_ code formatter for JavaScript in your settings. See the [configuration](../configuring-zed.md) documentation for more information.

For example, if you have Prettier installed and on your `PATH`, you can use it to format JavaScript files by adding the following to your `settings.json`:

```json
{
  "languages": {
    "JavaScript": {
      "formatter": {
        "external": {
          "command": "prettier",
          "arguments": ["--stdin-filepath", "{buffer_path}"]
        }
      }
    }
  }
}
```

## JSX

Zed supports JSX syntax highlighting out of the box.

In JSX strings, the [`tailwindcss-language-server`](./tailwindcss.md) is used provide autocompletion for Tailwind CSS classes.

## JSDoc

Zed supports JSDoc syntax in JavaScript and TypeScript comments that match the JSDoc syntax. Zed uses [tree-sitter/tree-sitter-jsdoc](https://github.com/tree-sitter/tree-sitter-jsdoc) for parsing and highlighting JSDoc.

## ESLint

You can configure Zed to format code using `eslint --fix` by running the ESLint
code action when formatting:

```json
{
  "languages": {
    "JavaScript": {
      "code_actions_on_format": {
        "source.fixAll.eslint": true
      }
    }
  }
}
```

You can also only execute a single ESLint rule when using `fixAll`:

```json
{
  "languages": {
    "JavaScript": {
      "code_actions_on_format": {
        "source.fixAll.eslint": true
      }
    }
  },
  "lsp": {
    "eslint": {
      "settings": {
        "codeActionOnSave": {
          "rules": ["import/order"]
        }
      }
    }
  }
}
```

> **Note:** the other formatter you have configured will still run, after ESLint.
> So if your language server or prettier configuration don't format according to
> ESLint's rules, then they will overwrite what ESLint fixed and you end up with
> errors.

If you **only** want to run ESLint on save, you can configure code actions as
the formatter:

```json
{
  "languages": {
    "JavaScript": {
      "formatter": {
        "code_actions": {
          "source.fixAll.eslint": true
        }
      }
    }
  }
}
```

### Configure ESLint's `nodePath`:

You can configure ESLint's `nodePath` setting:

```json
{
  "lsp": {
    "eslint": {
      "settings": {
        "nodePath": ".yarn/sdks"
      }
    }
  }
}
```

### Configure ESLint's `problems`:

You can configure ESLint's `problems` setting.

For example, here's how to set `problems.shortenToSingleLine`:

```json
{
  "lsp": {
    "eslint": {
      "settings": {
        "problems": {
          "shortenToSingleLine": true
        }
      }
    }
  }
}
```

### Configure ESLint's `rulesCustomizations`:

You can configure ESLint's `rulesCustomizations` setting:

```json
{
  "lsp": {
    "eslint": {
      "settings": {
        "rulesCustomizations": [
          // set all eslint errors/warnings to show as warnings
          { "rule": "*", "severity": "warn" }
        ]
      }
    }
  }
}
```

## See also

- [Yarn documentation](./yarn.md) for a walkthrough of configuring your project to use Yarn.
- [TypeScript documentation](./typescript.md)
