JavaScript Best Practices

Write clean, safe and fast JavaScript.

✍️ 3 exercises + code challenge in this lesson

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Use const by default and let when a value must change. Avoid var.
Always use === and !==.
Give variables and functions clear, descriptive names.
Keep functions small: each should do one thing.
Avoid global variables; use modules and block scope.
Handle errors with try...catch around risky code (network, JSON parsing).
Use textContent for user-provided text to avoid XSS attacks.
Cache DOM lookups you use often instead of querying repeatedly.
Use a linter (ESLint) and a formatter (Prettier) to keep code consistent.

Key Takeaways: JavaScript Best Practices

Mastering JavaScript Best Practices helps you write clean and reliable JavaScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

JavaScript Best Practices Code Example

JavaScript

<pre id="out"></pre>
<script>
const log = (...a) => document.getElementById("out").textContent += a.join(" ") + "\n";
// ❌ Hard to read
// var a = function(x){ if(x == "1") return true }

// ✅ Clear and safe
const isFirstPlace = (position) => position === 1;

const results = [3, 1, 2];
const winnerIndex = results.findIndex(isFirstPlace);
log("Winner is player", winnerIndex + 1);
</script>

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JavaScript Best Practices Practice Exercises

Check what you learned in “JavaScript Best Practices”.

/ 3 solved

Fill in the blank

Use strict equality.

if (count  0) { }

✓ Correct! Not quite. Try again.

Multiple choice

Which declaration should you use by default?

const var let global

✓ Correct! Not quite. Try again.

Code challenge

Rewrite the code so it logs "Valid" using === instead of ==. The value is the number 5.

Write the code in the live editor. Your answer is checked automatically.

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JavaScript Best Practices

💡 Key Takeaways: JavaScript Best Practices

JavaScript Best Practices Code Example

JavaScript Best Practices Practice Exercises

Key Takeaways: JavaScript Best Practices