My Favorite 10 JavaScript One-Liners That Save Time Daily

🧠 Introduction

As developers, we’re constantly looking for ways to write cleaner, shorter, and more efficient code. Over time, I’ve picked up some powerful JavaScript one-liners that help me speed up development, simplify logic, and even impress teammates during code reviews.

In this post, I’ll share my 10 favorite JavaScript one-liners I use regularly — with real examples and tips for when to use them.

🔟 1. Remove Duplicates from an Array

const unique = [...new Set([1, 2, 2, 3, 4, 4])]; 
// [1, 2, 3, 4]

✅ Great for cleaning up data or ensuring unique values in a form or filter.

9️⃣ 2. Swap Two Variables

[a, b] = [b, a];

✅ Simple and clean — no temp variable needed.

8️⃣ 3. Short-Circuit Default Values

const name = user.name || "Guest";

✅ A quick fallback if a value is undefined or falsy.

7️⃣ 4. Check if a Number is Even

const isEven = num => num % 2 === 0;

✅ Works great inside conditionals, filters, or validators.

6️⃣ 5. Flatten an Array

const flat = arr.flat(Infinity);

✅ Removes all levels of nesting in one go.

5️⃣ 6. Generate a Random Hex Color

const color = '#' + Math.floor(Math.random()*16777215).toString(16);

✅ Perfect for random themes, gradients, or creative UIs.

4️⃣ 7. Count Occurrences in an Array

const count = arr.reduce((a, v) => (a[v] = (a[v] || 0) + 1, a), {});

✅ Handy for analytics, tagging systems, or filtering results.

3️⃣ 8. Get the Last Item of an Array

const last = arr.at(-1);

✅ Cleaner than arr[arr.length - 1].

2️⃣ 9. Capitalize the First Letter

const cap = str => str.charAt(0).toUpperCase() + str.slice(1);

✅ Great for formatting names, titles, or headings.

1️⃣ 10. Delay with Promises

const wait = ms => new Promise(res => setTimeout(res, ms));

✅ Useful for delays in async flows, animations, or retries.

📌 Final Thoughts

These one-liners aren’t just clever tricks — they’re practical tools I use in real projects.
By mastering these patterns, you’ll not only write less code, but also improve your ability to think functionally and write expressively in JavaScript.

🚀 Try using 2–3 of these in your next project and feel the difference!

💬 Got your own favorite one-liner? Drop it in the comments and let’s build the ultimate list!
🔁 Save this post for future quick wins in your daily coding!