Adopting linters and formatters: ESLint, Prettier, etc.

Anton Ioffe - October 27th 2023 - 9 minutes read

In the realm of modern web development, gaining mastery over code quality tools like linters and formatters can truly set you apart as a JavaScript developer. This comprehensive guide will delve into the intricacies of JavaScript linters including ESLint and formatters such as Prettier, demonstrating how they demand crisp, clean code that adheres to best practices. Moreover, it will provide insights on the subtle art of effectively deploying these tools, their comparative efficacy, common pitfalls, and expert tricks to maximize their potential. The discussion will extend beyond just ESLint and Prettier, bringing into the spotlight other remarkable tools in this domain. As we navigate through code snippets, comparative analyses, and tool-specific tips, prepare for an illuminating journey on improving your JavaScript code quality through competent use of these indispensable tools.

Understanding Linters and Formatters: An Overview

Linters and formatters play a formidable role in the realm of JavaScript development. Linters, such as ESLint, primarily aid in enhancing your code quality. They go about this by analyzing your code against a set of predefined or custom rules, known as rulesets in ESLint. These rules help maintain a uniform coding style across your team, reducing inconsistency-related bugs and enhancing readability.

On the flip side, formatters like Prettier enforce a consistent style throughout your codebase. They parse your code and reprint it according to their own rules, respecting your code editor's maximum line length and wrapping code wherever necessary. The core advantage of using a formatter is the alleviated need for debates on code styling, as the formatter handles this uniformly.

To demonstrate the utility of these tools, take a hypothetical JavaScript project that lacks a concrete style guide and rules. Its coding style might show variation across the project, and there could be unused variables and required dependencies scattered around. Introducing a linter and formatter in such a scenario would ensure the enforcement of a consistent coding style, uncover potential bugs, and maintain a clean, easy-to-read codebase.

To sum up, the concurrent use of linters and formatters, like ESLint and Prettier, brings significant benefits to JavaScript development. While ESLint concentrates on upholding coding standards, detecting code quality issues, and spotting potential bugs, Prettier ensures the automated formatting of your code to maintain consistency. The collaborative use of these tools simplifies the overall development process, reduces errors, and leads to more maintainable, high-quality code. It's crucial to see these not as alternatives but complementary tools, each with their distinct purposes and advantages.

Exploring ESLint: Best Practices and Common Mistakes

ESLint, arguably the most popular JavaScript linting tool, thrives primarily on two key strengths: finding issues within your code and fixing them automatically. This impressively practical tool is either built into most text editors or can be integrated as extensions, validating its widespread popularity. Customization is one of ESLint’s specialties; you can build upon the default rules and create custom rules to fit your project's needs. For instance, consider the following rule which flags any unused variables:

rules: {
    'no-unused-vars': ['error', { 'args': 'none' }]

Despite the benefits, there are common pitfalls when adopting ESLint. A typical mistake is an improper setup, mainly due to the complex nature of its configurations. When you initiate ESLint with npx eslint --init, it poses a series of questions for configuration. Beginners might struggle to grasp implications and therefore select unsuitable settings for their needs. Thus, a best practice is to start with basic configurations, then progressively expand upon the ESLint rules according to the project's demands. It's also advisable to periodically revisit your ESLint configurations and adjust them as the project evolves.

The comparison between ESLint and Prettier often gives the false impression that they are substitutes. While ESLint does an excellent job as a linter and does have formatting capabilities, Prettier is specifically purposed as a code formatter. Hence, it's beneficial to use them in combination to leverage their combined strengths. This might seem redundant, but it provides more robustness. By implementing ESLint for enforcing code quality rules and Prettier for formatting, you enhance overall code quality and readability significantly.

Ensuring that ESLint is part of your continuous integration pipeline is of utmost importance. It is not a tool to use sporadically, but instead should be fully integrated into your development workflow. You need it to detect issues early in the development process, which otherwise could have escalated further down the line. A good practice is to trigger ESLint checks before committing code. This setup can be as straightforward as adding an npm script like "lint": "eslint \"**/*.js\".

Think of your journey with ESLint as a series of ongoing improvements rather than a one-time setup. Practice makes ESLint work for you, ultimately enhancing the quality of your project's code and maintaining coding standards. Remember, the role of ESLint is not to complicate your coding process, but to aid you in producing the best code possible.

Mastering Prettier: Achieving Cleaner Code

Mastering Prettier revolves around understanding the tool's primary function - to enhance code readability by dispensing a regular coding style. To facilitate systematization, Prettier disregards the original formatting and reprints an optimized syntax adhering to its rules. It's important to note, though, Prettier isn't entirely inflexible. Despite enforcing a specific set of rules, options to slightly adjust it according to your project's needs are available. For instance, you can add configuration options to a .prettierrc.json file in your project's root directory.

As an example of Prettier's capabilities, let's take a look at a poorly formatted code snippet:

let name='John';let age=22;if( age > 21 ) { console.log( 'Allowed' );}else {   console.log( 'Not Allowed' );  }

Running this code block through Prettier significantly enhances its readability:

let name = 'John';
let age = 22;
if (age > 21) {
} else {
    console.log('Not Allowed');

As seen here, Prettier added spaces around variables and operators, correctly placed semicolons and broke down long lines into readable chunks.

To integrate Prettier into your projects, you can install it with the command npm install --save-dev --save-exact prettier. To check and correct the formatting of your whole project, you would use the commands npx prettier --check . and npx prettier --write . respectively. By doing so, Prettier will scan your JavaScript files, check them against its formatting rules, and rewrite files that it deems incorrectly formatted.

One common mistake developers should avoid when using Prettier is ignoring built-in editor integrations. Prettier can format your code automatically as you write it when combined with an IDE plugin. This setup provides immediate feedback and guarantees a consistent codebase formatted according to the rules prescribed by the team. Hence, allowing developers to focus more on solving problems than aligning codes. All in all, adopting and mastering Prettier can significantly simplify the coding process and result in clean, readable, and consistent code.

A Comparative Analysis: ESLint and Prettier

ESLint and Prettier serve two distinct, yet complementary roles in modern web development. ESLint is a widely adopted linter for JavaScript that primarily focuses on identifying and reporting on patterns within your code. It excels at enforcing coding standards, identifying potential bugs in code quality, and communicating these discrepancies to the developer, aiding in real-time code debugging.

The strength of ESLint lies in its configuration flexibility, allowing for the creation of project-specific rules. It can readily be integrated with popular IDEs to provide on-the-fly feedback, and auto-fixing capabilities where possible. Due to its nature as a static code analysis tool, one key consideration is the potentially higher complexity and slight performance impact ESLint may introduce, especially for large codebases or during continuous integration processes.

On the other hand, Prettier serves as an opinionated code formatter. Unlike ESLint, Prettier focuses on automatically formatting the code to ensure consistency in appearance. It takes the original styling of the code, parses it, and then reprints it according to its own set of rules, ensuring a consistent style across the codebase. This takes the burden of styling and readability conventions away from the developer. As Prettier focuses purely on code formatting, it is generally less complex and lighter on memory utilization compared to ESLint. One potential downside is that Prettier's out-of-the-box configurations might not suit all project needs, and adjusting the rules might introduce some complexity.

Integration of ESLint and Prettier often leads to promising results. Both can be integrated to work in tandem, with Prettier handling code format and ESLint focusing on code quality rules. This combination mitigates their respective limitations, providing developers with a powerful toolset that promotes robust, clean, and readable code. The decision to adopt both, in the end, boils down to the specific needs of your project and how much you value elements like code consistency and bug detection.

Lastly, the question for the reader: Have you experienced other benefits or drawbacks of using ESLint and Prettier in your projects? Are there any notable situations where you found one tool to be more useful over the other?

Beyond ESLint and Prettier: Other Linting and Formatting Tools

Let's explore a few alternatives to ESLint and Prettier, starting with JSHint and JSLint. Both are linting tools like ESLint, with their own sets of rules and capabilities. What makes JSLint unique is its stringent ruleset, created and maintained by Douglas Crockford, a well-known figure in the JavaScript community. Its unforgiving nature towards any code that doesn't meet its strict standards makes it a fantastic tool for those who wish to follow Crockford's best practices strictly. On the other hand, JSHint, a fork of JSLint, offers customizable rules, making it more flexible and forgiving, akin to ESLint. JSHint though, doesn't display the rule causing an error which can make tracking down the issue a bit more challenging.

Next, we delve into Beautify, a code formatter akin to Prettier. Popular among HTML, CSS and JS developers, Beautify provides broad customizability for coding styles. You get to decide how your code should look and it obliges! This flexibility, however, results in more setup time and a potentially inconsistent style if team members have different preferences. Despite this, Beautify can be an excellent tool for those who like a significant degree of control over their code format.

Let's look closer at a few code mistakes these tools can help to avoid. For instance, using '==' instead of '===' is a frequent slip-up in JavaScript. While it might not always cause a problem, it can lead to unexpected type coercion. JSLint, with its strict approach, helps nip such issues in the bud by enforcing the use of '===' instead. Similarly, Beautify can help correct issues related to code readability. Indentation issues, long lines of code, and improper line breaks can all make code hard to read and understand. Beautify can correct these issues, reprinting the code according to the rules you've set, thus improving its readability considerably.

Each of these tools has unique strengths and can be more beneficial in specific situations, contributing to the code quality in its way. JSLint, with its strict rules, is well-suited to a developer or team looking to rigorously adhere to Crockford's coding standards. Conversely, JSHint offers flexibility that can suit teams who wish to define their own standards, while still benefiting from a robust linting tool. Beautify is an excellent choice for those who wish to micromanage their code's formatting aspects and are prepared to invest the setup time. Ultimately, the selection between ESLint, Prettier, JSLint, JSHint or Beautify depends on the specific needs, size, and preferences of your team. Remember, the goal of using such tools should be creating clean, maintainable, and robust JavaScript code.


In this article, the author explores the importance of adopting linters and formatters like ESLint and Prettier in modern web development. They emphasize the benefits of using these tools together, rather than viewing them as substitutes. The article provides an overview of linters and formatters, discusses best practices and common mistakes when using ESLint and Prettier, compares the two tools, and explores other alternatives. The key takeaway is that by leveraging these code quality tools, developers can improve code consistency, readability, and maintainability.

Challenging Technical Task: As a senior-level developer, take the time to review your current JavaScript projects and assess whether you are using linters and formatters effectively. Evaluate the effectiveness of your code quality tools and consider how you can optimize your processes to maximize their potential. Experiment with different configurations and rulesets to find the best fit for your projects. Share your experiences and insights with your team to promote continuous improvement and the adoption of best practices.

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