Generating HTML with JavaScript has always been ugly. Hella ugly. It usually involves writing streams of hard-to-maintain code which just concatenates a bunch of strings together and spits them out in an ugly mess.
Wouldn’t it be awesome if we could do something pretty like this:
div(
h1("Some title"),
p("Some exciting paragraph text"),
br(),
ul(
li("First item"),
li("Second item"),
li("Third item")
)
);
And have it output something beautiful like this:
<div>
<h1>Some title</h1>
<p>Some exciting paragraph text</p>
<br />
<ul>
<li>First item</li>
<li>Second item</li>
<li>Third item</li>
</ul>
</div>
With Jaml, we can do exactly that. Jaml is a simple library inspired by the excellent Haml library for Ruby. It works by first defining a template using an intuitive set of tag functions, and then rendering it to appear as pretty HTML. Here’s an example of how we’d do that with the template above:
Jaml.register('simple', function() {
div(
h1("Some title"),
p("Some exciting paragraph text"),
br(),
ul(
li("First item"),
li("Second item"),
li("Third item")
)
);
});
Jaml.render('simple');
All we need to do is call Jaml.register with a template name and the template source. Jaml then stores this for later use, allowing us to render it later using Jaml.render(). Rendering with Jaml gives us the nicely formatted, indented HTML displayed above.
So we’ve got a nice way of specifying reusable templates and then rendering them prettily, but we can do more. Usually we want to inject some data into our template before rendering it – like this:
Jaml.register('product', function(product) {
div({cls: 'product'},
h1(product.title),
p(product.description),
img({src: product.thumbUrl}),
a({href: product.imageUrl}, 'View larger image'),
form(
label({'for': 'quantity'}, "Quantity"),
input({type: 'text', name: 'quantity', id: 'quantity', value: 1}),
input({type: 'submit', value: 'Add to Cart'})
)
);
});
In this example our template takes an argument, which we’ve called product. We could have called this anything, but in this case the template is for a product in an ecommerce store so product makes sense. Inside our template we have access to the product variable, and can output data from it.
Let’s render it with a Product from our database:
//this is the product we will be rendering
var bsg = {
title : 'Battlestar Galactica DVDs',
thumbUrl : 'thumbnail.png',
imageUrl : 'image.png',
description: 'Best. Show. Evar.'
};
Jaml.render('product', bsg);
The output from rendering this template with the product looks like this:
<div class="product">
<h1>Battlestar Galactica DVDs</h1>
<p>Best. Show. Evar.</p>
<img src="thumbnail.png" />
<a href="image.png">View larger image</a>
<form>
<label for="quantity">Quantity</label>
<input type="text" name="quantity" id="quantity" value="1"></input>
<input type="submit" value="Add to Cart"></input>
</form>
</div>
Cool – we’ve got an object oriented declaration of an HTML template which is cleanly separated from our data. How about we define another template, this time for a category which will contain our products:
Jaml.register('category', function(category) {
div({cls: 'category'},
h1(category.name),
p(category.products.length + " products in this category:"),
div({cls: 'products'},
Jaml.render('product', category.products)
)
);
});
Our category template references our product template, achieving something rather like a partial in Ruby on Rails. This obviously allows us to keep our templates DRY and to easily render a hypothetical Category page like this:
//here's a second product
var snowWhite = {
title : 'Snow White',
description: 'not so great actually',
thumbUrl : 'thumbnail.png',
imageUrl : 'image.png'
};
//and a category
var category = {
name : 'Doovde',
products: [bsg, snowWhite]
}
Jaml.render('category', category);
All we’ve done is render the ‘category’ template with our ‘Doovde’ category, which contains an array of products. These were passed into the ‘product’ template to produce the following output:
<div class="category">
<h1>Doovde</h1>
<p>2 products in this category:</p>
<div class="products"><div class="product">
<h1>Battlestar Galactica DVDs</h1>
<p>Best. Show. Evar.</p>
<img src="thumbnail.png" />
<a href="image.png">View larger image</a>
<form>
<label for="quantity">Quantity</label>
<input type="text" name="quantity" id="quantity" value="1"></input>
<input type="submit" value="Add to Cart"></input>
</form>
</div>
<div class="product">
<h1>Snow White</h1>
<p>not so great actually</p>
<img src="thumbnail.png" />
<a href="image.png">View larger image</a>
<form>
<label for="quantity">Quantity</label>
<input type="text" name="quantity" id="quantity" value="1"></input>
<input type="submit" value="Add to Cart"></input>
</form>
</div>
</div>
</div>
You can see live examples of all of the above at http://edspencer.github.com/jaml.
Jaml currently sports a few hacks and is not particularly efficient. It is presented as a proof of concept, though all the output above is true output from the library. As always, all of the code is up on Github, and contributions are welcome 🙂
Jaml would be suitable for emulating a Rails-style directory structure inside a server side JavaScript framework – each Jaml template could occupy its own file, with the template name coming from the file name. This is roughly how Rails and other MVC frameworks work currently, and it eliminates the need for the Jaml.register lines. Alternatively, the templates could still be stored server side and simply pulled down and evaluated for client side rendering.
Happy rendering!
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Ed Spencer 
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