JavaScript Best Practices

Code Quality

Use const by default for all variables that don't need to be reassigned, and use let only when you need to change the value later. This practice makes your code more predictable and easier to reason about because you know which values can change and which can't. const prevents accidental reassignment bugs and signals intent to other developers. If you declare everything with const initially, you'll only change to let when you actually need to reassign, making your code clearer.

Avoid var entirely in modern JavaScript. var has confusing scoping rules (function scope instead of block scope), allows redeclaration without errors, and doesn't have a temporal dead zone like let and const. These quirks lead to bugs, especially for developers coming from other languages. There's no situation in modern JavaScript where var is better than const or let. Using const and let exclusively makes your code more predictable and easier to maintain.

Always use strict equality (===) instead of loose equality (==). The loose equality operator performs type coercion, which leads to surprising and inconsistent results: 0 == '' is true, 0 == '0' is true, but '' == '0' is false. These implicit conversions hide bugs and make code harder to understand. Strict equality checks both value and type without conversion, so you get predictable results. Similarly, use !== instead of != for inequality comparisons.

Use descriptive, meaningful variable names that explain what the variable represents, not just its type or a vague abbreviation. Good names like userCount, isAuthenticated, or maxRetries are self-documenting. Bad names like n, flag, or temp require you to read surrounding code to understand their purpose. While this makes code slightly longer to type, modern editors have autocomplete, and readable code is far more important than saving a few characters. Your code is read far more often than it's written.

Keep functions small and focused on a single task or responsibility. A function should do one thing well, not multiple unrelated operations. Small functions (typically 5-20 lines) are easier to understand, test, debug, and reuse. If a function is getting long or doing multiple things, break it into smaller helper functions with descriptive names. This single-responsibility principle makes code modular and maintainable. Function names should be verbs that clearly describe what the function does.

Add comments to explain why code does something, not what it does. The code itself should be clear enough to show what it's doing through good naming and structure. Comments are valuable for explaining non-obvious decisions, documenting known issues or edge cases, explaining complex algorithms, or warning about important constraints. Avoid obvious comments like // increment i or // set name to John. Instead, explain the reasoning: // Skip validation for admin users to improve performance or // Retry 3 times because the API occasionally returns 503 under load.

// Good: const by default
const MAX_USERS = 100;
const apiUrl = "https://api.example.com";

// Good: let for reassignment
let count = 0;
count++;

// Bad: var
// var x = 5;

// Good: strict equality
if (value === 0) {
  console.log("Zero");
}

// Bad: loose equality
// if (value == 0) {}

// Good: descriptive names
const userCount = 42;
const isAuthenticated = true;

// Bad: unclear names
// const n = 42;
// const flag = true;

Code Organization

Use arrow functions for callbacks in array methods, event handlers, and timers. Arrow functions are more concise and, crucially, don't create their own this binding—they inherit this from the surrounding scope. This eliminates the classic JavaScript this binding problem and makes callbacks more intuitive. However, use regular functions for object methods where you need this to refer to the object, and for any function that needs its own arguments object or might be used as a constructor.

Destructure objects and arrays to extract values into variables in a clean, readable way. Object destructuring lets you pull out specific properties: const { name, age } = person instead of const name = person.name; const age = person.age. Array destructuring extracts array elements: const [first, second] = colors. Destructuring reduces repetition, makes code more concise, and works great in function parameters to specify exactly which properties you need.

Use template literals (backticks) instead of string concatenation for any string that includes variables or expressions. Template literals make strings more readable and maintainable: `Hello, ${name}!` is clearer than 'Hello, ' + name + '!'. Template literals also support multi-line strings without \n escape sequences, and you can embed any JavaScript expression inside ${}. This makes generating HTML, SQL queries, or formatted messages much cleaner.

Use default parameters in function definitions to provide fallback values when arguments aren't passed. function greet(name = 'Guest') ensures name has a value even if called without arguments. This is cleaner and more explicit than checking for undefined inside the function: if (name === undefined) name = 'Guest'. Default parameters make function signatures self-documenting and prevent undefined errors. You can use expressions as defaults, even referencing earlier parameters.

Handle errors with try-catch blocks for operations that might fail, especially when parsing JSON, making network requests, or working with user input. Unhandled errors crash your program or leave it in an inconsistent state. try-catch lets you gracefully recover from errors, log them for debugging, and provide helpful feedback to users. Always catch errors from operations that can fail, but avoid wrapping every line in try-catch—only use it where errors are genuinely possible or expected.

Use async/await for working with promises instead of .then() chains. Async/await makes asynchronous code look and behave like synchronous code, which is much easier to read and reason about. async function fetchData() { const data = await fetch(url).then(r => r.json()); } is clearer than fetch(url).then(r => r.json()).then(data => ...). Async/await also makes error handling simpler with try-catch, and debugging is easier because stack traces are more meaningful. Always use await inside async functions, and remember that async functions always return promises.

// Arrow functions
const numbers = [1, 2, 3];
const doubled = numbers.map(n => n * 2);

// Destructuring
const person = { name: "John", age: 30 };
const { name, age } = person;

const colors = ["red", "green", "blue"];
const [first, second] = colors;

// Template literals
const greeting = `Hello, ${name}! You are ${age} years old.`;

// Default parameters
function greet(name = "Guest") {
  console.log(`Hello, ${name}`);
}

// Error handling
try {
  const data = JSON.parse(jsonString);
  console.log(data);
} catch (error) {
  console.error("Invalid JSON:", error.message);
}