What If React Had NO useEffect?

#react #typescript #nextjs #frontend

What If React Had NO useEffect? Building It From Scratch to Understand the WHY

Know WHY — Let AI Handle the HOW 🤖

Ever wondered why useEffect works the way it does? Let's think through this together by imagining React without useEffect and building our own solution step by step.

🎯 The Foundation: Everything Is Event-Driven

Your entire React app is just responding to events:

User clicks something → you handle it
API sends data → you handle it
Timer fires → you handle it

Simple, right? But here's where it gets interesting...

🧩 The Missing Piece

What if I want to "listen" to my props changing? Or my state updating?

There's no props.addEventListener('change') - props aren't DOM events. They're React's internal updates.

We need a way to subscribe to React's private changes.

🔨 Building Our Solution Step-by-Step

If we designed this subscription system from scratch, we'd need:

1️⃣ A callback function (what to do)

2️⃣ A condition (when to do it)

3️⃣ Timing control (before/after DOM updates)

That's literally what useEffect is!

🪤 The Closure Problem (Here's the WHY)

Now here's where things get really interesting...

When your effect runs, JavaScript creates a "snapshot" of all the values it uses. This is called a closure - it literally closes over those values.

But what happens when those values change in your component?

Your effect is still holding onto the OLD snapshot! It has no idea the values have updated.

💭 The Question This Raises:

How do we tell our effect: "Hey, get a fresh snapshot when these specific values change"?

We need a way to say:

"I want to subscribe to changes in THESE values specifically, and when they change, give me a new closure with the updated values."

✨ That's Exactly What the Dependency Array Solves!

It's like telling React:

"Watch these values for me. When any of them change, throw away my old closure and create a new one with fresh values."

useEffect(() => {
  // This closure captures current values
  console.log(`Current count: ${count}`);
}, [count]); // "Re-create this effect when count changes"