How to determine if vertical scroll bar has reache

问题:

The same question is answered in jQUery but I'm looking for solution without jQuery. How do you know the scroll bar has reached bottom of a page

I would like to know how I can determine whether vertical scrollbar has reached the bottom of the web page.

I am using Firefox3.6

I wrote simple Javascript loop to scroll down by 200 pixel and when the scroll bar reached the bottom of the page, I want to stop the loop.

The problem is scrollHeight() is returning 1989.

And inside loop scrollTop is incremented by 200 per iteration.

200 ==> 400 ==> 600 .... 1715

And from 1715, it won't increment so this loop continues forever.

Looks like scrollHeight() and scrollTop() is not right way to compare in order to determine the actual position of scrollbar? How can I know when the loop should stop?

code:

var curWindow = selenium.browserbot.getCurrentWindow();
var scrollTop = curWindow.document.body.scrollTop;
alert('scrollHeight==>' + curWindow.document.body.scrollHeight);

    while(curWindow.document.body.scrollHeight > curWindow.document.body.scrollTop) {
      scrollTop = curWindow.document.body.scrollTop;
      if(scrollTop == 0) { 
        if(window.pageYOffset) { //firefox
          alert('firefox'); 
          scrollTop = window.pageYOffset; 
        } 
        else { //IE
          alert('IE'); 
          scrollTop = (curWindow.document.body.parentElement) ? curWindow.document.body.parentElement.scrollTop : 0; 
        } 
      } //end outer if
      alert('current scrollTop ==> ' + scrollTop);
      alert('take a shot here'); 
      selenium.browserbot.getCurrentWindow().scrollBy(0,200);

    } //end while

回答1:

When you tell an element to scroll, if its scrollTop (or whatever appropriate property) doesn't change, then can't you assume that it has scrolled as far as is capable?

So you can keep track of the old scrollTop, tell it to scroll some, and then check to see if it really did it:

function scroller() {
    var old = someElem.scrollTop;
    someElem.scrollTop += 200;
    if (someElem.scrollTop > old) {
        // we still have some scrolling to do...
    } else {
        // we have reached rock bottom
    }
}

回答2:

I just read through the jQuery source code, and it looks like you'll need the "pageYOffset". Then you can get the window height and document height.

Something like this:

var yLeftToGo = document.height - (window.pageYOffset + window.innerHeight);

If yLeftToGo is 0, then you're at the bottom. At least that's the general idea.

回答3:

function scrollHandler(theElement){
   if((theElement.scrollHeight - theElement.scrollTop) + "px" == theElement.style.height)
       alert("Bottom");
}

For the HTML element (like div) add the event -- onscroll='scrollHandler(this)'.

回答4:

The correct way to check if you reached the bottom of the page is this:

1. Get document.body.clientHeight = the height of the ACTUAL screen shown
2. Get document.body.offsetHeight or document.body.scrollHeight = the height of the entire page shown
3. Check if document.body.scrollTop = document.body.scrollHeight - document.body.clientHeight

If 3 is true, you reached the bottom of the page

回答5:

Here is some code I've used to power infinite scrolling list views:

var isBelowBuffer = false;  // Flag to prevent actions from firing multiple times

$(window).scroll(function() {
    // Anytime user scrolls to the bottom
    if (isScrolledToBottom(30) === true) {
        if (isBelowBuffer === false) {
            // ... do something
        }
        isBelowBuffer = true;
    } else {
        isBelowBuffer = false;
    }
});

function isScrolledToBottom(buffer) {
    var pageHeight = document.body.scrollHeight;
    // NOTE:  IE and the other browsers handle scrollTop and pageYOffset differently
    var pagePosition = document.body.offsetHeight + Math.max(parseInt(document.body.scrollTop), parseInt(window.pageYOffset - 1));
    buffer = buffer || 0;
    console.log(pagePosition + "px / " + (pageHeight) + "px");
    return pagePosition >= (pageHeight - buffer);
}

回答6:

<span id="add"></add>

<script>
    window.onscroll = scroll;

    function scroll () {
    if (window.pageYOffset + window.innerHeight >= document.body.scrollHeight - 100) {
            document.getElementById("add").innerHTML += 'test<br />test<br />test<br />test<br />test<br />';
        }
    }
</script>