I think, answers to this question are too old... currently some desktop and mobile browsers support HTML Templates for doing this.
I've built a little example:
Tested OK in Chrome 61.0, Opera 48.0, Opera Neon 1.0, Android Browser 6.0, Chrome Mobile 61.0 and Adblocker Browser 54.0
Tested KO in Safari 10.1, Firefox 56.0, Edge 38.14 and IE 11
More compatibility info in canisue.com
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>HTML Template Example</title>
<link rel="stylesheet" href="styles.css">
<link rel="import" href="autoload-template.html">
</head>
<body>
<div class="template-container">1</div>
<div class="template-container">2</div>
<div class="template-container">3</div>
<div class="template-container">4</div>
<div class="template-container">5</div>
</body>
</html>
autoload-template.html
<span id="template-content">
Template Hello World!
</span>
<script>
var me = document.currentScript.ownerDocument;
var post = me.querySelector( '#template-content' );
var container = document.querySelectorAll( '.template-container' );
//alert( container.length );
for(i=0; i<container.length ; i++) {
container[i].appendChild( post.cloneNode( true ) );
}
</script>
styles.css
#template-content {
color: red;
}
.template-container {
background-color: yellow;
color: blue;
}
Your can get more examples in this HTML5 Rocks post