我想在窗口滚动速度超过某个值时触发一个事件。我找到了一些有助于测量速度的代码,但我无法弄清楚为什么当速度超过 150 时不触发 if
语句。任何帮助将不胜感激。
const checkScrollSpeed = (function(settings){
settings = settings || {};
let lastPos, newPos, timer, delta,
delay = settings.delay || 50;
function clear() {
lastPos = null;
delta = 0;
}
clear();
return function(){
newPos = window.scrollY;
if ( lastPos != null ){ // && newPos < maxScroll
delta = newPos - lastPos;
}
lastPos = newPos;
clearTimeout(timer);
timer = setTimeout(clear, delay);
return delta;
};
})();
const container = document.querySelector('#container');
window.addEventListener('scroll', function() {
console.log(checkScrollSpeed());
if (checkScrollSpeed() > 150) {
console.log('150+')
container.classList.add('red');
}
});
#container {
width: 75%;
height: 170vh;
background-color: yellow;
}
#container.red {
background-color: red !important;
}
<div id="container"></div>
您连续调用checkScrollSpeed
,当第二次调用时,delta 为 0。 删除console.log
或将 delta 分配给某个变量并将其用于日志记录和条件。
我认为
这是因为您在console.log
中第一次调用checkScrollSpeed()
和在if
语句中之间有一点延迟。您可以尝试仅调用一次,并保存 console.log
和 if
语句的值。它适用于我这个解决方案:
const checkScrollSpeed = (function(settings) {
settings = settings || {};
let lastPos, newPos, timer, delta,
delay = settings.delay || 50;
function clear() {
lastPos = null;
delta = 0;
}
clear();
return function() {
newPos = window.scrollY;
if (lastPos != null) { // && newPos < maxScroll
delta = newPos - lastPos;
}
lastPos = newPos;
clearTimeout(timer);
timer = setTimeout(clear, delay);
return delta;
};
})();
const container = document.querySelector('#container');
window.addEventListener('scroll', function() {
var speed = checkScrollSpeed();
console.log(speed);
if (speed > 150) {
console.log('150+');
container.classList.add('red');
}
});
#container {
width: 75%;
height: 170vh;
background-color: yellow;
}
#container.red {
background-color: red !important;
}
<div id="container"></div>