所以我试图使用JavaScript滚动调用一个函数。但是我想知道我是否可以不使用jQuery检测滚动的方向。如果没有，有什么变通办法吗?
我想只放一个“顶部”按钮，但如果可以的话，我想避免这个按钮。
我现在刚刚尝试使用这段代码，但它不起作用:
if document.body.scrollTop <= 0 {
alert ("scrolling down")
} else {
alert ("scrolling up")
}
当前回答
虽然公认的答案是可行的，但值得注意的是，这将以很高的速率发射。对于计算成本高的操作，这可能会导致性能问题。
MDN的建议是限制这些事件。下面是他们的样例的修改，增强检测滚动方向。
修改自:https://developer.mozilla.org/en-US/docs/Web/API/Document/scroll_event
// ## function declaration
function scrollEventThrottle(fn) {
let last_known_scroll_position = 0;
let ticking = false;
window.addEventListener("scroll", function () {
let previous_known_scroll_position = last_known_scroll_position;
last_known_scroll_position = window.scrollY;
if (!ticking) {
window.requestAnimationFrame(function () {
fn(last_known_scroll_position, previous_known_scroll_position);
ticking = false;
});
ticking = true;
}
});
}
// ## function invocation
scrollEventThrottle((scrollPos, previousScrollPos) => {
if (previousScrollPos > scrollPos) {
console.log("going up");
} else {
console.log("going down");
}
});
其他回答
你可以试试这样做。
function scrollDetect(){ var lastScroll = 0; window.onscroll = function() { let currentScroll = document.documentElement.scrollTop || document.body.scrollTop; // Get Current Scroll Value if (currentScroll > 0 && lastScroll <= currentScroll){ lastScroll = currentScroll; document.getElementById("scrollLoc").innerHTML = "Scrolling DOWN"; }else{ lastScroll = currentScroll; document.getElementById("scrollLoc").innerHTML = "Scrolling UP"; } }; } scrollDetect(); html,body{ height:100%; width:100%; margin:0; padding:0; } .cont{ height:100%; width:100%; } .item{ margin:0; padding:0; height:100%; width:100%; background: #ffad33; } .red{ background: red; } p{ position:fixed; font-size:25px; top:5%; left:5%; } <div class="cont"> <div class="item"></div> <div class="item red"></div> <p id="scrollLoc">0</p> </div>
虽然公认的答案是可行的，但值得注意的是，这将以很高的速率发射。对于计算成本高的操作，这可能会导致性能问题。
MDN的建议是限制这些事件。下面是他们的样例的修改，增强检测滚动方向。
修改自:https://developer.mozilla.org/en-US/docs/Web/API/Document/scroll_event
// ## function declaration
function scrollEventThrottle(fn) {
let last_known_scroll_position = 0;
let ticking = false;
window.addEventListener("scroll", function () {
let previous_known_scroll_position = last_known_scroll_position;
last_known_scroll_position = window.scrollY;
if (!ticking) {
window.requestAnimationFrame(function () {
fn(last_known_scroll_position, previous_known_scroll_position);
ticking = false;
});
ticking = true;
}
});
}
// ## function invocation
scrollEventThrottle((scrollPos, previousScrollPos) => {
if (previousScrollPos > scrollPos) {
console.log("going up");
} else {
console.log("going down");
}
});
捕捉所有滚动事件(触摸和滚轮)的简单方法
window.onscroll = function(e) {
// print "false" if direction is down and "true" if up
console.log(this.oldScroll > this.scrollY);
this.oldScroll = this.scrollY;
}
有时滚动行为不一致，不能正确更新元素的scrollTop属性。在决定滚动方向之前设置一些阈值会更安全。
let lastScroll = 0
let threshold = 10 // must scroll by 10 units to know the direction of scrolling
element.addEventListener("scroll", () => {
let newScroll = element.scrollTop
if (newScroll - lastScroll > threshold) {
// "up" code here
} else if (newScroll - lastScroll < -threshold) {
// "down" code here
}
lastScroll = newScroll
})
这是对prateek的回答的补充。在IE的代码中似乎有一个小故障，所以我决定修改它一点也不花哨(只是另一个条件)
$('document').ready(function() {
var lastScrollTop = 0;
$(window).scroll(function(event){
var st = $(this).scrollTop();
if (st > lastScrollTop){
console.log("down")
}
else if(st == lastScrollTop)
{
//do nothing
//In IE this is an important condition because there seems to be some instances where the last scrollTop is equal to the new one
}
else {
console.log("up")
}
lastScrollTop = st;
});});
