window.scrollTop 未定义

Question

为什么 window.scrollTop 未定义？

https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollTop

The Element.scrollTop property gets or sets the number of pixels that an element's content is scrolled vertically.

An element's scrollTop value is a measurement of the distance from the element's top to its topmost visible content. When an element's content does not generate a vertical scrollbar, then its scrollTop value is 0.

jQuery(window).on('scroll', function() {
        if(window.scrollTop > 0) {
            console.log('of the top')
            console.log('scroll top value is: ' + window.scrollTop)
        } else {
            console.log('the top')
            console.log('scroll top value is: ' + window.scrollTop)
        }
    })

我在控制台日志中得到的是：

scroll top value is: undefined

而且我总是在 if else 中得到一个评估：

of the top

即使我滚动到页面顶部。

为什么 window.scrollTop 未定义？

https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollTop window 不算元素吗？

Answer 1

您需要使用 jQuery $ 标识符以及 .scrollTop() 的括号 () 才能获得位置

这是可执行代码：

<script>
jQuery(window).on('scroll', function() {
        if($(window).scrollTop() > 0) {
            console.log('of the top')
            console.log('scroll top value is: ' + $(window).scrollTop())
        } else {
            console.log('the top')
            console.log('scroll top value is: ' + $(window).scrollTop())
        }
    })
</script>

Answer 2

<script>
jQuery(window).on('scroll', function() {
        if($(window).scrollTop() > 0) {
            console.log('of the top')
            console.log('scroll top value is: ' + $(window).scrollTop())
        } else {
            console.log('the top')
            console.log('scroll top value is: ' + $(window).scrollTop())
        }
    })
</script>

YESSINE 的代码是正确的。但可以让它变得简单

<script>
jQuery(window).on('scroll', function() {
        var window = $(window);
        if(window.scrollTop() > 0) {                
            console.log('of the top')
            console.log('scroll top value is: ' + window.scrollTop())
        } else {
            console.log('the top')
            console.log('scroll top value is: ' + window.scrollTop())
        }
    })
</script>

window.scrollTop 未定义

window.scrollTop is undfined

javascript

jquery

scroll