[Javascript] An Accordion Menu with Minimal Code

In this article, we will explain how to implement multiple accordion menus without using external libraries, and provide demos for reference.


Implementing accordion open-close animations in raw JavaScript can become complex, but we aim to keep the code concise.

⓪Requirements

We aim to implement accordions with minimal code, but without compromising on functionality.
We intend to meet the following requirements typically expected from standard accordions.

• Add opening and closing animations
• Allow specifying the initial open/close state on access
• Change the direction of the arrow when it’s open and closed
• Ensure smooth functionality even with multiple instances of the accordion

From this point, we will provide a detailed explanation step by step. However, if you prefer not to have explanations and would like to see the complete source code, you can skip directly to the full source code from here.

①Prepare the components of the accordion menu in HTML

First, prepare the button and content for the accordion menu in HTML.

<div class="accordion-btn">Accordion Button</div>
<div class="accordion-content">
    <p>Accordion Content</p>
</div>

②Implement the open-close functionality in JavaScript.

We use forEach to ensure it works with multiple accordions.
Additionally, we set the necessary styles for the open-close functionality in JavaScript rather than CSS for clarity.
The event registration for opening and closing content on button click is done in line 6.

document.querySelectorAll('.accordion-btn').forEach(function(el){
    const next = el.nextElementSibling
    const nextH = next.scrollHeight + 'px'
    next.style.overflow = 'hidden'
    next.style.height = 0
    el.onclick = () => next.style.height = el.classList.toggle('open') ? nextH : 0)
})

We put demo up to this point. It currently fulfills 1 out of 4 requirements.

• Add opening and closing animations
• Allow specifying the initial open/close state on access
• Change the direction of the arrow when it’s open and closed
• Ensure smooth functionality even with multiple instances of the accordion

③Refine the appearance with CSS

Let’s style the appearance using CSS for clarity.
Note that the padding specified in line 7 should be applied to the elements inside the content, not the content itself, to prevent any visual distortion.

.accordion-btn {
    cursor: pointer;
    background: skyblue;
    padding: 10px;
}
.accordion-content p{
    padding: 10px;
}

④Add opening and closing animations

To add open-close animations, you just need to specify a transition on the accordion content.

document.querySelectorAll('.accordion-btn').forEach(function(el){
    const next = el.nextElementSibling
    const nextH = next.scrollHeight + 'px'
    next.style.overflow = 'hidden'
    next.style.transition = '0.5s' // added
    next.style.height = 0
    el.onclick = () => next.style.height = el.classList.toggle('open') ? nextH : 0
})

We put demo up to this point. It currently fulfills 2 out of 4 requirements.

• Add opening and closing animations
• Allow specifying the initial open/close state on access
• Change the direction of the arrow when it’s open and closed
• Ensure smooth functionality even with multiple instances of the accordion

⑤Allow specifying the initial open/close state on access

There may be cases where you want a specific accordion menu to be open from the start. Let’s make it so that if the accordion button has the “open” class, it will be in the open state.

document.querySelectorAll('.accordion-btn').forEach(function(el){
    const next = el.nextElementSibling
    const nextH = next.scrollHeight + 'px'
    next.style.overflow = 'hidden'
    next.style.transition = '0.5s'
    next.style.height = el.classList.contains("open") ? nextH : 0   // modified
    el.onclick = () => next.style.height = el.classList.toggle('open') ? nextH : 0
})

By adding the “open” class to the accordion button you want to keep open from the start, the content will be displayed in the open state by default.

<div class="accordion-btn open">Accordion Button</div>  <!-- modified -->
<div class="accordion-content">
    <p>Accordion Content</p>
</div>
<div class="accordion-btn">Accordion Button</div>
<div class="accordion-content">
    <p>Accordion Content</p>
</div>

We put demo up to this point. It currently fulfills 3 out of 4 requirements.

• Add opening and closing animations
• Allow specifying the initial open/close state on access
• Change the direction of the arrow when it’s open and closed
• Ensure smooth functionality even with multiple instances of the accordion

⑥Change the direction of the arrow when it’s open and closed

Typically, accordions have arrows or some visual indicators on the buttons for clarity.
Finally, let’s make sure to display different arrows for when it’s open and when it’s closed.

We will use the CSS ::after pseudo-element to display each arrow on the far right of the accordion button.

.accordion-btn::after{
    content: '▼';
    float: right;
}
.accordion-btn.open::after{
    content: '▲';
}

We put demo up to this point. It now meets all of the specified requirements

• Add opening and closing animations
• Allow specifying the initial open/close state on access
• Change the direction of the arrow when it’s open and closed
• Ensure smooth functionality even with multiple instances of the accordion

The full text of source code

In the end, I put the full text of source code.

<style>
    .accordion-btn {
        cursor: pointer;
        background: skyblue;
        padding: 10px;
    }
    .accordion-content p{
        padding: 10px;
    }
    .accordion-btn::after{
        content: '▼';
        float: right;
    }
    .accordion-btn.open::after{
        content: '▲';
    }
</style>

<div class="accordion-btn">Accordion Button</div>
<div class="accordion-content">
    <p>Accordion Content</p>
</div>

<script>
    document.querySelectorAll('.accordion-btn').forEach(function(el){
        const next = el.nextElementSibling
        const nextH = next.scrollHeight + 'px'
        next.style.overflow = 'hidden'
        next.style.transition = '0.5s'
        next.style.height = el.classList.contains("open") ? nextH : 0
        el.onclick = () => next.style.height = el.classList.toggle('open') ? nextH : 0
    })
</script>

That is all, it was about how to implement accordions with minimal code.