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无限下拉.html
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无限下拉.html
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<!DOCTYPE html>
<html>
<head>
<title></title>
<style type="text/css">
.box {
background-color: rgba(40, 40, 190, 255);
border: 4px solid rgb(20, 20, 120);
transition: background-color 1s, border 1s;
width: 350px;
height: 350px;
display: flex;
align-items: center;
justify-content: center;
padding: 20px;
}
.vertical {
color: white;
font: 32px "Arial";
}
.extra {
width: 350px;
height: 350px;
margin-top: 10px;
border: 4px solid rgb(20, 20, 120);
text-align: center;
padding: 20px;
}
</style>
</head>
<body>
<div>
<ul>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
</ul>
</div>
<div class="box" id="box">
<div class="vertical">
Welcome to <strong>The Box!</strong>
</div>
</div>
<div>
<ul>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
<li>asdf</li>
</ul>
</div>
<div class="box" id="box2">
<div class="vertical">
Welcome to <strong>The Box2!</strong>
</div>
</div>
</body>
<script type="text/javascript">
const numSteps = 20.0;
let prevRatio = 0.0;
let increasingColor = "rgba(40, 40, 190, ratio)";
let decreasingColor = "rgba(190, 40, 40, ratio)";
// Set things up
window.addEventListener("load", (event) => {
let target = document.querySelector("#box");
let target2 = document.querySelector("#box2");
createObserver(target);
createObserver(target2)
}, false);
function createObserver(target) {
let observer;
let options = {
root: null,
rootMargin: "0px",
// threshold: buildThresholdList()
// threshold: 1
threshold: [0,.5,1]
};
observer = new IntersectionObserver(handleIntersect, options);
observer.observe(target);
}
function buildThresholdList() {
let thresholds = [];
let numSteps = 20;
for (let i=1.0; i<=numSteps; i++) {
let ratio = i/numSteps;
thresholds.push(ratio);
}
thresholds.push(0);
return thresholds;
}
function handleIntersect(entries, observer) {
entries.forEach((entry) => {
console.log(entry.intersectionRatio)
if (entry.intersectionRatio > prevRatio) { // 出现在viewport中的比例提高还是减少
entry.target.style.backgroundColor = increasingColor.replace("ratio", entry.intersectionRatio);
} else {
entry.target.style.backgroundColor = decreasingColor.replace("ratio", entry.intersectionRatio);
}
prevRatio = entry.intersectionRatio;
});
}
</script>
</html>