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CSS实现渐隐渐现效果.md

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CSS Implementation of Fade In and Fade Out Effect

Implementing a fade in and fade out effect is a common way to enhance user interaction. The usual approach is to toggle the display property value between none and other values. While this method achieves the desired functionality, the effect can appear abrupt and rigid. Therefore, there is a demand for a smoother transition when elements disappear.

Implementation

opacity

The opacity property is used to set the transparency of an element. Simply setting opacity to 0 visually hides the element, but it still occupies its original position and affects the layout of the webpage. It will also respond to user interactions such as click events. To add animation effects, we can use the transitionend event to listen for the completion of the transition and then hide the element. Additionally, the transparent visual effect of the opacity property can be exploited for clickjacking attacks.

<!DOCTYPE html>
<html>
<head>
    <title>opacity</title>
    <style type="text/css">
        .page{
            width: 200px;
            padding: 10px 20px;
            border: 1px solid #eee;
        }
        .container {
            overflow: hidden;
        }
        .container > .options{
            opacity: 1;
            transition: all .5s;
        }
        .container > .btn{
            color: #4C98F7;
            cursor: pointer;
            text-decoration: underline;
        }
        .container > .hide{
            display: none;
        }
        .container > .fold{
            opacity: 0;
        }
    </style>
</head>
<body>
    <div class="page">
        <div class="container">
            <div class="btn" onclick="operate(this)" unfold="1">Hide</div>
            <div class="options">
                <div class="option">Option 1</div>
                <div class="option">Option 2</div>
                <div class="option">Option 3</div>
                <div class="option">Option 4</div>
                <div class="option">Option 5</div>
                <div class="option">Option 6</div>
                <div class="option">Option 7</div>
            </div>
        </div>
    </div>
</body>
<script type="text/javascript">
    function operate(btn){
        const optionsNode = document.querySelector(".container > .options");
        const unfold = btn.getAttribute("unfold");
        if(unfold && unfold==="1"){
            btn.innerText = "Open";
            optionsNode.classList.add("fold");
            const finish = () => {
                optionsNode.classList.add("hide");
                optionsNode.removeEventListener("transitionend", finish); // Remove the listener
            }
            optionsNode.addEventListener("transitionend", finish); // Add the listener
        }else{
            btn.innerText = "Hide";
            optionsNode.classList.remove("hide");
            setTimeout(() => optionsNode.classList.remove("fold"));
        }
        btn.setAttribute("unfold", unfold === "0" ? "1" : "0");
    }
</script>
</html>

visibility opacity

When the visibility property value is set to hidden, the element will be hidden but still occupy its own space and affect the layout of the webpage. Unlike opacity, it does not respond to any user interactions and will also be hidden in screen reading software. If the visibility of a child element is set to visible while the visibility of its parent element is set to hidden, the child element will still be visible while the parent element is hidden. This property requires a browser version of IE 9 or above for compatibility.

Furthermore, when transitioning from visibility: hidden; to visibility: visible;, if a transition time of 3s is set, the element will not immediately show the transition effect from hidden to visible after the event occurs. Instead, it will wait for 3s and then instantly hide, making the total time from display to final disappearance 3s. However, the transition is not gradual. Therefore, in order to achieve a transition effect, we usually use it together with opacity.

<!DOCTYPE html>
<html>
<head>
    <title>opacity</title>
    <style type="text/css">
        .page{
            width: 200px;
            padding: 10px 20px;
            border: 1px solid #eee;
        }
        .container {
            overflow: hidden;
        }
        .container > .options{
            opacity: 1;
            visibility: visible;
            transition: all .5s;
        }
        .container > .btn{
            color: #4C98F7;
            cursor: pointer;
            text-decoration: underline;
        }
        .container > .hide{
            display: none;
        }
        .container > .fold{
            opacity: 0;
            visibility: hidden;
        }
    </style>
</head>
<body>
    <div class="page">
        <div class="container">
            <div class="btn" onclick="operate(this)" unfold="1">Hide</div>
            <div class="options">
                <div class="option">Option 1</div>
                <div class="option">Option 2</div>
                <div class="option">Option 3</div>
                <div class="option">Option 4</div>
                <div class="option">Option 5</div>
                <div class="option">Option 6</div>
                <div class="option">Option 7</div>
            </div>
        </div>
    </div>
</body>
<script type="text/javascript">
    function operate(btn){
        const optionsNode = document.querySelector(".container > .options");
        const unfold = btn.getAttribute("unfold");
        if(unfold && unfold==="1"){
            btn.innerText = "Open";
            optionsNode.classList.add("fold");
            const finish = () => {
                optionsNode.classList.add("hide");
                optionsNode.removeEventListener("transitionend", finish); // Remove the listener
            }
            optionsNode.addEventListener("transitionend", finish); // Add the listener
        }else{
            btn.innerText = "Hide";
            optionsNode.classList.remove("hide");
            setTimeout(() => optionsNode.classList.remove("fold"));
        }
        btn.setAttribute("unfold", unfold === "0" ? "1" : "0");
    }
</script>
</html>


## Daily Question

https://github.com/WindrunnerMax/EveryDay


## References

https://juejin.cn/post/6844903497998024711 https://www.cnblogs.com/MrZhujl/p/10315177.html https://blog.csdn.net/u012767761/article/details/87369414