Monday, November 16, 2009

Building a Product List Service: HTML Templating

Along with the product list service itself, I built a demo page. The first iteration of this page was very simple: a table to display list entries, a visible form to add new entries, and some invisible forms for generating update/delete requests. Even with this primitive page, however, I ran into the problem of how to turn the JSON data from the service into HTML.

My first approach was “the simplest thing that could possibly work”: I wrote a JavaScript function that built up an HTML string from the JSON, and then inserted this string into DIV using innerHTML. It worked, and had the benefit that the various event handlers were defined in the same file — if I changed a function's name or interface, I didn't have to update multiple files. But embedding markup in a script is ugly and hard to maintain; just keeping quotes matched takes a lot of work.

My second approach was to develop a utility library containing functions that build markup based on model objects. This approach was clearly influenced by Swing; in fact, the object passed to my buildTable() function looked a lot like Swing's TableModel. Doing this got the markup out of my main script, and gave me reusable components, which I liked. However, the code defining the model object alone was larger than my original concatenation function.

If my second approach resembled Swing, my first approach resembled early servlets. Keeping with the Java analogies, what I was really looking for was an approach that resembled JSP: all markup within one file, making references to data provided elsewhere.

With some pointers from friends who are adept JavaScript programmers, I started looking at different templating solutions. John Resig's micro-templates even looked like JSP directives (which meant, unfortunately, that they couldn't be used within a JSP-generated page). I tried out a few of the existing solutions, then decided to write my own — it was only a dozen lines of code, using regular expressions.

But while the template approach did the job, and provided a fairly clean break between markup and scripts, I was still uncomfortable. In part because there was now too much of a break between the markup and the scripts that interacted with it: a script in one file would blindly access markup from another file. My JavaScript friends would say that this break is a Good Thing, but I think that it ignores the fact that the markup and scripts are tightly coupled by nature — and in fact takes us back to a 1960s view of programs manipulating data. But hat's a topic for a future post.

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