[css] CSS 3 slide-in from left transition

Use CSS3 2D transform to avoid performance issues (mobile)

A common pitfall is to animate left/top/right/bottom properties instead of using to achieve the same effect. For a variety of reasons, the semantics of transforms make them easier to offload, but left/top/right/bottom are much more difficult.

Source: Mozilla Developer Network (MDN)


Demo:

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var $slider = document.getElementById('slider');
var $toggle = document.getElementById('toggle');

$toggle.addEventListener('click', function() {
    var isOpen = $slider.classList.contains('slide-in');

    $slider.setAttribute('class', isOpen ? 'slide-out' : 'slide-in');
});
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#slider {
    position: absolute;
    width: 100px;
    height: 100px;
    background: blue;
    transform: translateX(-100%);
    -webkit-transform: translateX(-100%);
}

.slide-in {
    animation: slide-in 0.5s forwards;
    -webkit-animation: slide-in 0.5s forwards;
}

.slide-out {
    animation: slide-out 0.5s forwards;
    -webkit-animation: slide-out 0.5s forwards;
}
    
@keyframes slide-in {
    100% { transform: translateX(0%); }
}

@-webkit-keyframes slide-in {
    100% { -webkit-transform: translateX(0%); }
}
    
@keyframes slide-out {
    0% { transform: translateX(0%); }
    100% { transform: translateX(-100%); }
}

@-webkit-keyframes slide-out {
    0% { -webkit-transform: translateX(0%); }
    100% { -webkit-transform: translateX(-100%); }
}
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<div id="slider" class="slide-in">
    <ul>
        <li>Lorem</li>
        <li>Ipsum</li>
        <li>Dolor</li>
    </ul>
</div>

<button id="toggle" style="position:absolute; top: 120px;">Toggle</button>
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