JavaScript Type Inference in NetBeans

Roman Strobl has just published a screencast of the new JavaScript editor in NetBeans 6.1. The demo is around 5 minutes and highlights many of the editing features. I'd like to dwell on the type inference part a bit. Around four minutes into the demo, Roman shows that NetBeans figures out the types of expressions, including those involving function calls. In his example, all the types happened to be Strings so it may look like a lucky coincidence. It's not! Here's some code fragments showing in more detail what's going on. Let's start with a jQuery expression in an HTML file - in my last entry I showed how code completion already helps you fill in the strings inside the jQuery dollar function. NetBeans knows the return type of the dollar function so we're only presented with jQuery methods here: jQuery methods return the jQuery object itself as the return value, so we can chain calls into jQuery. We'll do that here by calling a function on the return value from addClass: As you can see, when NetBeans knows the return type of a function, it's shown in code completion item separated by a colon. Here I want to call the queue() method which returns an array of functions. Let's see what happens if we just call functions on the result object: As you can see - we're getting methods on the Array class, since we're getting an array back. Let's pick a specific element in the array instead, and see what code completion g...

Date: April, 29 2008
Url: http://blogs.sun.com/tor/entry/javascript_type_inference

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