JavaScript Micro-Templating
I’ve had a little utility that I’ve been kicking around for some time now that I’ve found to be quite useful in my JavaScript application-building endeavors. It’s a super-simple templating function that is fast, caches quickly, and is easy to use. I have a couple tricks that I use to make it real fun to mess with.
Here’s the source code to the templating function (a more-refined version of this code will be in my upcoming book Secrets of the JavaScript Ninja):
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// Simple JavaScript Templating(function(){
var
cache = {};
this.tmpl = function
tmpl(str, data){
// Figure out if we‘re getting a template, or if we need to
// load the template - and be sure to cache the result.
var
fn = !/\W/.test(str) ?
cache[str] = cache[str] ||
tmpl(document.getElementById(str).innerHTML) :
// Generate a reusable function that will serve as a template
// generator (and which will be cached).
new
Function("obj",
"var p=[],print=function(){p.push.apply(p,arguments);};"
+
// Introduce the data as local variables using with(){}
"with(obj){p.push(‘"
+
// Convert the template into pure JavaScript
str
.replace(/[\r\t\n]/g, " ")
.split("<%").join("\t")
.replace(/((^|%>)[^\t]*)‘/g, "$1\r")
.replace(/\t=(.*?)%>/g, "‘,$1,‘")
.split("\t").join("‘);")
.split("%>").join("p.push(‘")
.split("\r").join("\\‘")
+ "‘);}return p.join(‘‘);");
// Provide some basic currying to the user
return
data ? fn( data ) : fn;
};
})();You would use it against templates written like this
(it doesn’t have to be in
this particular manner – but it’s a style that I enjoy):
<script type="text/html"
id="item_tmpl">
<div id="<%=id%>"
class="<%=(i % 2 == 1 ? "
even" : "")%>">
<div class="grid_1 alpha right">
<img class="righted"
src="<%=profile_image_url%>"/>
</div>
<div class="grid_6 omega contents">
<p><b><a href="/<%=from_user%>"><%=from_user%></a>:</b> <%=text%></p>
</div>
</div>
</script> |
You can also inline script:
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<script type="text/html"
id="user_tmpl">
<% for
( var
i = 0; i < users.length; i++ ) { %>
<li><a href="<%=users[i].url%>"><%=users[i].name%></a></li>
<% } %>
</script> |
Quick tip: Embedding scripts in your page that have a unknown content-type (such is the case here – the browser doesn’t know how to execute a text/html script) are simply ignored by the browser – and by search engines and screenreaders. It’s a perfect cloaking device for sneaking templates into your page. I like to use this technique for quick-and-dirty cases where I just need a little template or two on the page and want something light and fast.
and you would use it from script like so:
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var
results = document.getElementById("results");
results.innerHTML = tmpl("item_tmpl", dataObject);
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You could pre-compile the results for later use. If you call the templating function with only an ID (or a template code) then it’ll return a pre-compiled function that you can execute later:
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var
show_user = tmpl("item_tmpl"), html = "";
for
( var
i = 0; i < users.length; i++ ) {
html += show_user( users[i] );
} |
The biggest falling-down of the method, at this point, is the
parsing/conversion code – it could probably use a little love. It does use one
technique that I enjoy, though: If you’re searching and replacing through a
string with a static search and a static replace it’s faster to perform the
action with .split("match").join("replace") – which seems
counter-intuitive but it manages to work that way in most modern browsers.
(There are changes going in place to grossly improve the performance
of.replace(/match/g, "replace") in the next version of Firefox
– so the previous statement won’t be the case for long.)
Feel free to have fun with it – I’d be very curious to see what mutations occur with the script. Since it’s so simple it seems like there’s a lot that can still be done with it.