Why You Should Stop Using `innerHTML +=` and Switch to `insertAdjacentHTML()`

If you’ve ever dynamically added HTML in JavaScript, you’ve probably used innerHTML like this:

document.getElementById("container").innerHTML += "<div>New item</div>";

But did you know this approach has major downsides?

• ❌ It destroys existing event listeners
• ❌ Resets form inputs and dynamic states
• ❌ Hurts performance with large DOM updates

Luckily, there’s a better way: insertAdjacentHTML()!

What’s Wrong with innerHTML +=?

When you use innerHTML +=, the browser:

1. Serializes the entire container’s HTML into a string
2. Appends your new HTML
3. Re-parses everything and recreates the DOM

This means:

• All existing event listeners are wiped out
• JavaScript references to elements break
• Form inputs lose their values

Example of the Problem

// Add a button with a click listener
const container = document.getElementById("container");
container.innerHTML = `<button id="btn">Click Me</button>`;
document.getElementById("btn").addEventListener("click", () => alert("Clicked!"));

// Later, append more HTML (this BREAKS the listener!)
container.innerHTML += "<div>New content</div>";
// Now, the button’s click handler is GONE!

insertAdjacentHTML() to the Rescue!

This method lets you insert HTML at specific positions without destroying the existing DOM.

Syntax

element.insertAdjacentHTML(position, htmlString);

Four Insertion Positions

Why It’s Better

✅ Preserves event listeners (no DOM rebuild)

✅ Faster performance (no full re-parse)

✅ More control over placement

Practical Example: Dynamic List Updates

❌ Bad Way (innerHTML +=)

const list = document.getElementById("todo-list");
list.innerHTML += `<li>New Task</li>`; // Wipes existing listeners!

✅ Better Way (insertAdjacentHTML)

const list = document.getElementById("todo-list");
list.insertAdjacentHTML("beforeend", `<li>New Task</li>`); // Safe!

✅ Best Way (With Event Delegation)

// Insert safely
list.insertAdjacentHTML("beforeend", `<li class="task">New Task</li>`);

// Handle clicks via delegation (works even for new items)
document.addEventListener("click", (e) => {
  if (e.target.classList.contains("task")) {
    e.target.classList.toggle("completed");
  }
});

When Should You Use It?

✔ Appending dynamic content (chat messages, todos, etc.)

✔ Avoiding DOM reset side effects

✔ Optimizing frequent DOM updates

When Should You Avoid It?

✖ If you need to replace an entire element (use innerHTML or replaceWith())

✖ If inserting unsanitized HTML (risk of XSS—always sanitize first!)

Performance Comparison

insertAdjacentHTML() is much faster than innerHTML += because it doesn’t:

• Re-serialize the entire container
• Destroy and recreate DOM nodes

Benchmark Example

// Slow: innerHTML +=
for (let i = 0; i < 1000; i++) {
  container.innerHTML += `<div>Item ${i}</div>`;
}

// Fast: insertAdjacentHTML
for (let i = 0; i < 1000; i++) {
  container.insertAdjacentHTML("beforeend", `<div>Item ${i}</div>`);
}

Final Thoughts

• Stop using innerHTML +=—it’s destructive and slow.
• Use insertAdjacentHTML('beforeend', ...) for safe, efficient DOM updates.
• Combine with event delegation for bulletproof dynamic elements.

Try It Yourself!

Next time you dynamically add HTML, replace innerHTML += with insertAdjacentHTML() and see the difference!