this question means to change the placeholder of img by clicking on the a link, but add the onclick event in HTML and return false still appears the page jump situation, also according to the night check but did not find any problems, please take a look! Here is the code
<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>Image Gallery</title>
</head>
<body>
<h1>Snapshots</h1>
<ul>
<li>
<a href="images/fireworks.jpg" title="A fireworks display" onclick="showPic(this);return false">Fireworks</a>
</li>
<li>
<a href="images/coffee.jpg" title="A cup of black coffee" onclick="showPic(this);return false;">Coffee</a>
</li>
<li>
<a href="images/rose.jpg" title="A red, red rose" onclick="showPic(this);renturn false;">Rose</a>
</li>
<li>
<a href="images/bigben.jpg" title="The famous clock" onclick="showPic(this);return false;">Big Ben</a>
</li>
</ul>
<img id="placeholder" src=" " alt="my imgage gallery">
<p id="description">Choose an image.
</body>
<script>
function showPic ( whichpic){
var source = whichpic.getAttibute("href");
var placeholder = document.getElementById( "placeholder");
placeholder.setAttribute( "src",source);
var text = whichpic.getAttibute( "title" );
var description = document.getElementById("description");
description.firstChild.nodeValue = text;
}
function countBodyChildren(){
var body_element = document.getElementsByTagName( "body")[0];
console.log ( body_element.childNodes.length);
}
window.onload = countBodyChildren;
</script>
</html>