Oxc Formatter Vs. Prettier: Nesting Await Statements

When it comes to code formatters, consistency and predictability are key. Both Prettier and oxc are popular choices for JavaScript and TypeScript projects, aiming to automate code formatting according to a defined style. However, differences can arise, especially in complex scenarios like deeply nested await statements within long lines. This article delves into a specific case where the oxc formatter and Prettier exhibit divergent behavior, providing insights into the nuances of each tool and how they handle intricate code structures.

Understanding the Issue: Nested Await Statements

The core of the matter lies in how these formatters deal with nested await expressions, particularly when they are part of a longer chain of method calls. Consider the following TypeScript code snippet:

{
  const x = async (xxxxxxxx: string): Promise<void> => {
    await (await (await xxxx.xxxx.x(xxxxxxxxxxxxxxx))?.xxxxxxxxxxxx())
      ?.xxxxxxx(xxxxxxxx)
      .xxxxxxxx();
  };
}

This code features a function x that makes several asynchronous calls. It showcases a series of nested await expressions, where the result of one await is immediately used in another. The optional chaining operator (?.) further adds to the complexity, ensuring that subsequent calls are made only if the preceding value is not null or undefined. The challenge for a code formatter is to maintain readability while adhering to the specified line width and code style.

Prettier's Approach

Prettier, known for its opinionated formatting style, aims to enforce consistency across codebases. When faced with the above code, Prettier version 3.6.2 leaves the code untouched:

{
  const x = async (xxxxxxxx: string): Promise<void> => {
    await (await (await xxxx.xxxx.x(xxxxxxxxxxxxxxx))?.xxxxxxxxxxxx())
      ?.xxxxxxx(xxxxxxxx)
      .xxxxxxxx();
  };
}

This indicates that Prettier deems the original formatting acceptable, even though the line length is substantial. It prioritizes keeping the nested await expressions on a single line, likely to preserve the visual flow of the chained calls.

oxc Formatter's Approach

The oxc formatter, on the other hand, takes a different approach. Version 0.15 introduces line breaks to improve readability:

{
  const x = async (xxxxxxxx: string): Promise<void> => {
    await (
      await (await xxxx.xxxx.x(xxxxxxxxxxxxxxx))?.xxxxxxxxxxxx()
    )
      ?.xxxxxxx(xxxxxxxx)
      .xxxxxxxx();
  };
}

The oxc formatter inserts a line break after the first await expression, effectively separating the nested await calls. This formatting choice aims to reduce line length and enhance clarity, particularly for developers who prefer shorter lines and more explicit structure.

Analyzing the Differences

The divergence in formatting stems from the distinct philosophies and algorithms employed by Prettier and the oxc formatter. Prettier tends to be more conservative in introducing line breaks, often prioritizing horizontal compactness unless a line exceeds the specified printWidth by a significant margin or there are clear syntactic boundaries that suggest a break. The oxc formatter, in this case, appears to be more aggressive in breaking up long expressions, even if they don't strictly violate the printWidth limit. This could be due to a specific rule or heuristic within the oxc formatter that targets nested await expressions or chained calls.

Configuration Considerations

Both Prettier and the oxc formatter offer configuration options to tailor their behavior. The provided config.json file outlines the settings used in this scenario:

{
  "printWidth": 100,
  "tabWidth": 2,
  "useTabs": false,
  "semi": true,
  "singleQuote": true,
  "quoteProps": "as-needed",
  "jsxSingleQuote": false,
  "trailingComma": "all",
  "bracketSpacing": true,
  "bracketSameLine": false,
  "arrowParens": "always"
}

The printWidth is set to 100 characters, which means that the formatter should ideally keep lines within this limit. However, as demonstrated, the formatters may interpret this guideline differently. There isn't a specific configuration in either tool that directly controls the formatting of nested await expressions. Achieving the desired formatting often involves a combination of settings and, in some cases, manual adjustments.

Implications and Best Practices

The differences in formatting can have implications for team collaboration and code review processes. If a team uses a mix of Prettier and the oxc formatter, or if developers have different configurations, inconsistencies can arise. To mitigate this, it's crucial to:

1. Establish a consistent formatting strategy: Decide on a single formatter and configuration for the entire project.
2. Integrate the formatter into the development workflow: Use editor integrations, pre-commit hooks, or CI/CD pipelines to automatically format code.
3. Communicate formatting preferences: Discuss and document any specific formatting rules or exceptions within the team.
4. Consider maintainability: Favor formatting that enhances readability and reduces cognitive load, even if it means deviating slightly from the default settings.

In the specific case of nested await expressions, it's often beneficial to introduce line breaks to improve clarity. While Prettier might not do this automatically, the oxc formatter's approach can serve as a starting point. Developers can further refine the formatting manually if needed, ensuring that the code remains both functional and easy to understand.

Conclusion

The divergence between Prettier and the oxc formatter in handling nested await statements highlights the complexities of code formatting. While both tools aim to automate the process, their underlying algorithms and philosophies can lead to different outcomes. Understanding these nuances is essential for developers to make informed choices and maintain consistency across their projects. By carefully considering configuration options and establishing clear formatting guidelines, teams can leverage these tools to enhance code quality and collaboration.

For more information on code formatting best practices, consider exploring resources like the Airbnb JavaScript Style Guide. It offers comprehensive recommendations on various aspects of JavaScript coding style, including formatting.