HTML

How to create collapsable using pure Javascript

const collapsableBtn = document.querySelectorAll('.collapsable-toggle');

for (let index = 0; index < collapsableBtn.length; index++) {
    collapsableBtn[index].addEventListener('click', function(e) {
        // e.preventDefault();
        e.stopImmediatePropagation();

        iterateElement = this;

        getCollapsableParent = iterateElement.parentElement;

        if(getCollapsableParent.classList.contains('show')) {
            getCollapsableParent.classList.remove('show')
            iterateElement.innerText = iterateElement.getAttribute('data-onCloseText');

        } else {
            getCollapsableParent.classList.add('show');
            iterateElement.innerText = iterateElement.getAttribute('data-onOpenText');
        }
    })
}

How to create collapsable using pure Javascript

.collapsable-container #expand {
   display:none;
}
.collapsable-container.show #expand {
    display:block;
}

How to create collapsable using pure Javascript

<div class="collapsable-container">
    <a href="javascript:void(0);" class="collapsable-toggle" data-onOpenText="Hide First Content" data-onCloseText="Show First Content">Show First Content</a>
    <div id="expand">
        This is some Content
    </div>
 </div>
 
 
 <div class="collapsable-container">
    <a href="javascript:void(0);" class="collapsable-toggle" data-onOpenText="Hide Second Content" data-onCloseText="Show Second Content">Show Second Content</a>
    <div id="expand">
        This is some Content
    </div>
 </div>