Determine whether the element is visible in at least half of the viewport

Question

Determine whether the element is visible in at least half of the viewport

I am working on a project that involves 4 cards with images. I want the image to animate in from the left when it comes into viewport. I have finalized the CSS for this effect, but the JavaScript code always returns false even when the element is visible on the screen. I specifically want the function to return true when at least half of the image is in the viewport. Despite using a forEach loop to check all images, the function keeps returning false.

Below is the JavaScript code snippet I have developed:

function isInViewport(container) {
  const rect = container.getBoundingClientRect();
  
  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
    rect.right <= (window.innerWidth || document.documentElement.clientWidth)
  );
}

This is the HTML structure I am using:

<div class="col-md-6 col-sm-12 p-0 overflow-hidden bg-dark imageCard">
  <div class="imageCont">
    <img
      src="images/ferrariPhoto1.webp"
      alt=""
      style="width: 100%; height: 100%"
      class="ferrariImageSection"
    />
  </div>
</div>

javascript html css

Answer 1

Answer №1

I created a simple demonstration using your function on codepen, and it appears that the function is performing correctly: https://codepen.io/lukenetsurfer/pen/WNPzQdO

This demo showcases a blue square that can be dragged across the screen. By checking the console, you can observe the output of isInViewport every time the square is moved. When the square is only partially visible (partially off-screen), isInViewport returns false; otherwise, it returns true.

Here are some debugging suggestions to help identify why it may not be working in your case:

If you console.log container, does it display the expected value? (Perhaps you are inspecting the wrong element?)
If you console.log the values involved in your boolean comparison, do they align with your expectations?

Answer 2

I created a simple demonstration using your function on codepen, and it appears that the function is performing correctly: https://codepen.io/lukenetsurfer/pen/WNPzQdO

This demo showcases a blue square that can be dragged across the screen. By checking the console, you can observe the output of isInViewport every time the square is moved. When the square is only partially visible (partially off-screen), isInViewport returns false; otherwise, it returns true.

Here are some debugging suggestions to help identify why it may not be working in your case:

If you console.log container, does it display the expected value? (Perhaps you are inspecting the wrong element?)
If you console.log the values involved in your boolean comparison, do they align with your expectations?

Answer 3

Answer №2

Check out the Intersection Observer as suggested by Darryl Noakes.

I'm unable to provide specific help because the code in the question appears to be incomplete and lacks important details. The sample below showcases the use of IO with detailed comments.

const options = {
  root: null, // Default is null (html/viewport)
  rootMargin: "0px", // Default is 0 - values can be 1 to 4 numbers in px
  threshold: [0.25, 0.75]
  /* Threshold refers to the percentage of target element length that's visible */
};

/** Initialize Observer
 * Pass in callback function and options object.
 */
const observer = new IntersectionObserver(showHideTitle, options);

// Select all elements with class .card
const cards = document.querySelectorAll(".card");

// Apply observer to each .card element
cards.forEach(card => observer.observe(card));

/** Callback Function
 * When a .card is within thresholds (0.25 or 0.75),
 * this function is triggered.
 * Entries contain entry objects associated with target elements (.card).
 * Property .target returns the triggering element.
 * Property .intersectionRatio indicates the % of target element in viewport.
 */
function showHideTitle(entries, observer) {
  entries.forEach((entry) => {
    let text = entry.target.firstElementChild;
    if (entry.intersectionRatio > 0.75) {
      text.classList.add("fade-in");
      text.classList.remove("fade-out");
    } else {
      text.classList.remove("fade-in");
      text.classList.add("fade-out");
    }
  });
}

* {
  margin: 0;
  padding: 0;
}

:root {
  font: 5vmin/1 "Segoe UI";
}

body {
  display: flex;
  /* Other CSS properties removed for brevity */
}

/* Additional CSS styles omitted for clarity */

<ol id="list">
  <li class="card directions">
    <p class="text">Scroll to the right. &gt;</p>
  </li>
  <li class="card">
    <figure>
      <figcaption class="text">Lamborghini</figcaption>
      <img src="https://i.ibb.co/g3MmqLY/car1.png">
    </figure>
  </li>
  <li class="card directionless">>
    <!-- More list items here -->
  </li>
</ol>

Answer 4

Check out the Intersection Observer as suggested by Darryl Noakes.

I'm unable to provide specific help because the code in the question appears to be incomplete and lacks important details. The sample below showcases the use of IO with detailed comments.

const options = {
  root: null, // Default is null (html/viewport)
  rootMargin: "0px", // Default is 0 - values can be 1 to 4 numbers in px
  threshold: [0.25, 0.75]
  /* Threshold refers to the percentage of target element length that's visible */
};

/** Initialize Observer
 * Pass in callback function and options object.
 */
const observer = new IntersectionObserver(showHideTitle, options);

// Select all elements with class .card
const cards = document.querySelectorAll(".card");

// Apply observer to each .card element
cards.forEach(card => observer.observe(card));

/** Callback Function
 * When a .card is within thresholds (0.25 or 0.75),
 * this function is triggered.
 * Entries contain entry objects associated with target elements (.card).
 * Property .target returns the triggering element.
 * Property .intersectionRatio indicates the % of target element in viewport.
 */
function showHideTitle(entries, observer) {
  entries.forEach((entry) => {
    let text = entry.target.firstElementChild;
    if (entry.intersectionRatio > 0.75) {
      text.classList.add("fade-in");
      text.classList.remove("fade-out");
    } else {
      text.classList.remove("fade-in");
      text.classList.add("fade-out");
    }
  });
}

* {
  margin: 0;
  padding: 0;
}

:root {
  font: 5vmin/1 "Segoe UI";
}

body {
  display: flex;
  /* Other CSS properties removed for brevity */
}

/* Additional CSS styles omitted for clarity */

<ol id="list">
  <li class="card directions">
    <p class="text">Scroll to the right. &gt;</p>
  </li>
  <li class="card">
    <figure>
      <figcaption class="text">Lamborghini</figcaption>
      <img src="https://i.ibb.co/g3MmqLY/car1.png">
    </figure>
  </li>
  <li class="card directionless">>
    <!-- More list items here -->
  </li>
</ol>

Determine whether the element is visible in at least half of the viewport

Answer №1

Answer №2

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