Determine if an HTML element's content overflows

Overflow properties and their quirks

When dealing with the overflow property and its schizophrenic avatars (visible, hidden, scroll, or auto), things may go haywire. The visible form is quite the troublemaker as content can escape the box without triggering scrollWidth/scrollHeight. So, time to cook a stealthy workaround by temporarily hijacking the overflow property and setting it to hidden:

// Handling overflow stylings, because it's not always 'inside the box'
function frenzyOverflowDetect(element) {
  let prevOverflowStyle = element.style.overflow;
  if (!prevOverflowStyle || prevOverflowStyle === 'visible') {
    element.style.overflow = 'hidden'; // Force hide to measure overflow
  }
  let overflowStatus = element.scrollWidth > element.clientWidth || element.scrollHeight > element.clientHeight;
  // Rever the old overflow style because we respect 'privacy'
  element.style.overflow = prevOverflowStyle; 
  return overflowStatus; 
}


You've now successfully tamed the overflow beast.

Cross-browser compatibility: Easier said than done

In a diverse browser ecosystem, different rules apply to sizing and overflow. A few key steps can bring you closer to a universally effective overflow check:

1. Do feature detection, not browser detection. If a tree falls in a forest and no one is there to hear it, does it make a sound? Similarly, don't run code that a particular browser can't handle.

2. Embrace vendor prefixes when juggling CSS properties related to overflow and dimension.

3. And finally, test your code in different browsers. They're like snowflakes, no two are exactly alike.

Sneaky overflow and the case of the invisible scrollbars

Scrollbars, while helpful visual indicators, can also mislead you. Blame the designer, style guidelines, or users who just despise those thick scrollbars obstructing their view; sometimes, content runneth over but no scrollbar in sight. So we need a more reliable method:

// Overflow ended scrollbars' career, now hunts in the wild 🦁
function sneakyOverflowCheck(element) {
  return {
    horizontal: element.scrollWidth > element.offsetWidth,
    vertical: element.scrollHeight > element.offsetHeight
  };
}


Now you're prepared for wild, scrollbar-free overflow.

Conceptual visualization 🖼️

While we, programmers, are aliens to the visual world, let's honor our human side with a visual exercise. Imagine an HTML element is like a bucket. Too much content, it spills over.

| Bucket (HTML element)  | Content (Water)    | Overflow (Spill) |
|------------------------|--------------------|------------------|
| Fine                  | 🪣                 | None 🟢         |
| Overflow              | 🪣💧                | Yes! 🔴         |

JavaScript can help us check:

let bucket = document.querySelector('.bucket');
let isOverflowing = bucket.scrollHeight > bucket.clientHeight;


And the results:

- No overflow: 🪣🟢
- Overflow: 🪣💧🔴

So, just as a bucket has limits, so do HTML elements.

Proceed with caution: Edge cases and best practices

Overflow detection has some caveats:

1. Padding and Borders: Remember, clientWidth and clientHeight include padding but exclude borders. Overflows can happen if content plus padding exceeds the inner area of the element.

2. Non-visible Elements: Detecting overflow in invisible elements? 🙈 Wait until they show up on the page. Culprit? Incorrect dimensions of invisible elements.

3. Dynamic Content: If your content has a life of its own, event listeners or a **MutationObserver** can track changes in real-time.

4. Inline Elements: The rebel inline elements lacking scrollWidth and scrollHeight need some parental control. Wrap them in a block-level container to keep overflow in check.