slide-toggle: es6 vanilla javascript with SASS

slide-toggle-usage.html

<button class="js-slide-toggle__btn">toggle</button>
<div class="js-slide-toggle__content">
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Etiam sit amet orci eget eros faucibus tincidunt. Proin faucibus arcu quis ante. Sed aliquam ultrices mauris. Aenean viverra rhoncus pede. Donec interdum, metus et hendrerit aliquet, dolor diam sagittis ligula, eget egestas libero turpis vel mi.
</div>

slide-toggle.js

// Reference: http://jsfiddle.net/alistairjcbrown/wJTgA/

window.addEventListener('DOMContentLoaded', () => {
    const selector = 'js-slide-toggle';
    const buttonEl = document.querySelector(`.${selector}__btn`);
    const contentSelector = `${selector}__content`;

    if (buttonEl) {
        buttonEl.addEventListener('click', () => {
            document.querySelector(`.${contentSelector}`).classList.toggle(`${contentSelector}--expanded`);
        });
    }
});

slide-toggle.scss

.js-slide-toggle {
    &__content {
        max-height: 0;
        overflow: hidden;
        transition: max-height .5s ease-in-out;

        &--expanded {
            max-height: 10em;
        }
    }
}