header.html

<template id="solutionTemplate">
	<details>
		<summary>
			<span class="summary-title">Solution</span>
			<div class="summary-chevron">
				<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24"
					 viewBox="0 0 24 24" fill="none"
					 stroke="currentColor" stroke-width="2" stroke-linecap="round"
					 stroke-linejoin="round" class="feather">
					<polyline points="6 9 12 15 18 9"></polyline>
				</svg>
			</div>
		</summary>
		<div class="content"></div>
	</details>
</template>


<script>

class Accordion {
  constructor(el) {
    // Store the <details> element
    this.el = el;
    // Store the <summary> element
    this.summary = el.querySelector('summary');
    // Store the <div class="content"> element
    this.content = el.querySelector('.content');

    // Store the animation object (so we can cancel it if needed)
    this.animation = null;
    // Store if the element is closing
    this.isClosing = false;
    // Store if the element is expanding
    this.isExpanding = false;
    // Detect user clicks on the summary element
    this.summary.addEventListener('click', (e) => this.onClick(e));
  }

  onClick(e) {
    // Stop default behaviour from the browser
    e.preventDefault();
    // Add an overflow on the <details> to avoid content overflowing
    this.el.style.overflow = 'hidden';
    // Check if the element is being closed or is already closed
    if (this.isClosing || !this.el.open) {
      this.open();
    // Check if the element is being openned or is already open
    } else if (this.isExpanding || this.el.open) {
      this.shrink();
    }
  }

  shrink() {
    // Set the element as "being closed"
    this.isClosing = true;

    // Store the current height of the element
    const startHeight = `${this.el.offsetHeight}px`;
    // Calculate the height of the summary
    const endHeight = `${this.summary.offsetHeight}px`;

    // If there is already an animation running
    if (this.animation) {
      // Cancel the current animation
      this.animation.cancel();
    }

    // Start a WAAPI animation
    this.animation = this.el.animate({
      // Set the keyframes from the startHeight to endHeight
      height: [startHeight, endHeight]
    }, {
      duration: 400,
      easing: 'ease-out'
    });

    // When the animation is complete, call onAnimationFinish()
    this.animation.onfinish = () => this.onAnimationFinish(false);
    // If the animation is cancelled, isClosing variable is set to false
    this.animation.oncancel = () => this.isClosing = false;
  }

  open() {
    // Apply a fixed height on the element
    this.el.style.height = `${this.el.offsetHeight}px`;
    // Force the [open] attribute on the details element
    this.el.open = true;
    // Wait for the next frame to call the expand function
    window.requestAnimationFrame(() => this.expand());
  }

  expand() {
    // Set the element as "being expanding"
    this.isExpanding = true;
    // Get the current fixed height of the element
    const startHeight = `${this.el.offsetHeight}px`;
    // Calculate the open height of the element (summary height + content height)
    const endHeight = `${this.summary.offsetHeight + this.content.offsetHeight}px`;

    // If there is already an animation running
    if (this.animation) {
      // Cancel the current animation
      this.animation.cancel();
    }

    // Start a WAAPI animation
    this.animation = this.el.animate({
      // Set the keyframes from the startHeight to endHeight
      height: [startHeight, endHeight]
    }, {
      duration: 400,
      easing: 'ease-out'
    });
    // When the animation is complete, call onAnimationFinish()
    this.animation.onfinish = () => this.onAnimationFinish(true);
    // If the animation is cancelled, isExpanding variable is set to false
    this.animation.oncancel = () => this.isExpanding = false;
  }

  onAnimationFinish(open) {
    // Set the open attribute based on the parameter
    this.el.open = open;
    // Clear the stored animation
    this.animation = null;
    // Reset isClosing & isExpanding
    this.isClosing = false;
    this.isExpanding = false;
    // Remove the overflow hidden and the fixed height
    this.el.style.height = this.el.style.overflow = '';
  }
}

function obscureSolutions(selector = 'div.answer'){
  var solutions = document.querySelectorAll(selector);
  const template = document.getElementById("solutionTemplate");

  solutions.forEach(e => {
    let wrapped = template.content.cloneNode(true);
    wrapped.querySelector(".content").appendChild(e.cloneNode(true));
    e.replaceWith(wrapped);
  })
}

window.addEventListener("load", function() {
  // wrap answers in <details>
  // jquery is loaded anyways, so we could actually just use that instead
  obscureSolutions()

  document.querySelectorAll('details').forEach((el) => {
    new Accordion(el);
  });
});

</script>