JS capture page scroll bar-JS Tutorial-php.cn

JS capture page scroll bar

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Release： 2018-04-20 09:24:42

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This time I will bring you JS to capture the page scroll bar. What are the

Preface

In the process of writing a plug-in recently, I need to use JS to determine whether there is a scroll bar. Search After a while, the general methods are similar, but they are a bit verbose and the code is not concise enough. Finally, by referring to different methods, I wrote a relatively simple method. When judging the scroll bar, you also need to calculate the width of the scroll bar. I will share it with you through this article.

Why should we judge the scroll bar

The need to judge the scroll bar is often used in pop-up window plug-ins, because most pop-up windows will add

overflow<a href="http://www.php.cn/wiki/923.html" target="_blank">: hidden </a> attribute. If the page is relatively long, the page will shake after adding this attribute.

In order to enhance the user experience, add the

margin-left<a href="http://www.php.cn/wiki/937.html" target="_blank"> </a> attribute to offset the scroll bar after overflow: hidden

How to determine whether there is a scroll bar

In fact, only one line of JS is needed to test compatibility with IE7

function hasScrollbar() {
  return document.body.scrollHeight > (window.innerHeight || document.documentElement.clientHeight);
}

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Generally, use

document.body.scrollHeight > window.innerHeight

But in IE7 and IE8,

window.innerHeight underfined, so in order to be compatible with IE7 and IE8, you need to use document.documentElement.clientHeight

The method of calculating the scroll bar width

still takes the pop-up window as an example, because the scroll bars of IE 10 and above and mobile browsers do not occupy the page width. Transparent style (IE 10 and above browsers can restore the original scroll bar style through CSS properties), so in order to further enhance the user experience, we also need to calculate the width of the scroll bar and add a reasonable

margin-left ## according to the situation. #Value.

The method to calculate the width of the scroll bar is relatively simple. Create a new p element with a scroll bar and pass the

offsetWidth

Magnific-popup <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">function getScrollbarWidth() { var scrollp = document.createElement("p"); scrollp.style.cssText = 'width: 99px; height: 99px; overflow: scroll; position: absolute; top: -9999px;'; document.body.appendChild(scrollp); var scrollbarWidth = scrollp.offsetWidth - scrollp.clientWidth; document.body.removeChild(scrollp); return scrollbarWidth; }</pre><div class="contentsignin">Copy after login</div></div>

Summary

Use JS to implement a The function may not be difficult, but as programmers, you should always think about how to implement this function more simply and elegantly, and always focus on improving the user experience. For

conditional judgment

, maybe ten lines of logical judgment may only require one line. I have been deeply impressed recently, and I must be good at using ternary expressionsif..else The principle is to judge whether the document height is greater than the

visual area

height.