Code Review in JavaScript: What to Check and How to Give Feedback

Code Review in JavaScript: What to Check and How to Give Feedback

Code review is the process of checking code by one or more developers before it is merged into the main project branch. For beginner JavaScript developers (especially those working with Node.js), this is not just a formality, but a powerful tool for learning and improving quality. In this article, we will break down what to pay attention to during a review and how to formulate comments so as not to offend a colleague, but to help them grow.

Why is Code Review Important for JavaScript Projects?

JavaScript is a dynamic language, and errors often only appear at runtime. Code review helps to identify:

• Logical errors and bugs;
• Violations of architecture and code style;
• Performance issues;
• Security vulnerabilities (especially in Node.js).

Additionally, it's an excellent way to share knowledge within a team. Even if you are a beginner, your fresh perspective can spot things that an experienced developer might have missed.

What to Check in JavaScript Code: A Checklist

To make your review systematic, use the following checklist. It is divided into three blocks: correctness, readability, and performance/security.

1. Correctness and Logic

First, make sure the code solves the given task. Check:

• Edge cases: What happens if the array is empty? If the argument is null or undefined?
• Asynchrony: Are promises handled correctly? Is there any "callback hell" with nested .then() calls?
• Data types: Is strict equality used (=== instead of ==)?

// Bad: implicit type coercionif (userInput == 0) { ... }

// Good: strict comparisonif (userInput === 0) { ... }

2. Readability and Code Style

Code is written for people, not machines. Check:

• Naming: Variables and functions should speak for themselves. getData() is better than func1().
• Function size: A function should do only one thing. If it is longer than 20-30 lines, it might be worth breaking it up.
• Magic numbers: Extract numbers and strings into constants.

// Bad: magic numberif (status === 404) { ... }

// Good: named constantconst HTTP_NOT_FOUND = 404;if (status === HTTP_NOT_FOUND) { ... }

3. Performance and Security (Node.js)

For server-side JavaScript, this is critical:

• Avoid blocking the Event Loop: Heavy synchronous operations (e.g., JSON.parse of large data) are better done asynchronously or with workers.
• Error handling: Always use try/catch in async functions or .catch() for promises.
• Injections: Never concatenate user input directly into SQL or shell commands. Use parameterized queries.

// Bad: vulnerable to SQL injectionconst query = `SELECT * FROM users WHERE id = ${userId}`;

// Good: parameterized queryconst query = 'SELECT * FROM users WHERE id = $1';

How to Give Feedback: 5 Golden Rules

Even the most correct checklist is useless if the feedback makes the code author want to quit. Here is how to make a review constructive:

Rule 1: Start with the Positive

Find at least one thing that was done well. "Great solution with caching!" — this lifts the mood and shows that you are looking not only for mistakes.

Rule 2: Comment on the Code, Not the Person

Instead of "You wrote a terrible loop," write: "This loop can be replaced with Array.map() for better readability." Talk about