Libraries

Sequentially is a JavaScript library for asychronous programming. It makes it easy to define functions that are called later, or periodically, or that can be called only a certain number of times, or only at a certain frequency.

[code language=”javascript”]
// Call a function f five times in a row
f.only(5).repeatedly()
// Call f five times, at one second intervals
f.only(5).periodically()
// Make a new function g that calls through to f at most five times,
// no matter how often g is called
var g = f.only(5)
// Make a new function g that calls f at most once per minute,

Thanks to everyone who has commented or contributed, praised or pitched in — I’ve released an update to Functional Javascript, with these changes:

New features

- Rhino compatibility. I think — at least it loads now, and a couple of hand tests work; i have yet to port the testing tool. (Credit: Reginald Braithwaite)

Optimizations

- More efficient Array.slice. (Credit: Dean Edwards)
- Memoize Function.lambda. (Credit: henrah)

Functional is a JavaScript library for functional programming. It defines the standard higher-order functions (map, reduce, filter) that you can read about elsewhere on the web. It also defines functions for partial function application and function-level programming: curry, partial, compose, guard, and until. Finally, it introduces “string lambdas”, which let you write 'x -> x+1', 'x+1', or even '+1' as synonyms for function(x) {return x+1}.

JavaScript Gradient Roundrects adds gradient roundrects to an HTML page, without images. It uses the WHATWG canvas tag if it’s available. Otherwise it uses a stack of divs, whose heights are adaptively chosen according to the height of the graded element, the color components, and the radius curvature. There’s a demo here.

I also wrote a JavaScript CSS parser that lets you attach gradients to an element without writing code. You do this by including CSS inside a div tag whose class is ‘style’.

Last week for the first time I did some serious browser JavaScript programming. I put the following tools to good use, but ran against limits with each of them:

• fvLogger is terrific, but doesn’t include an evaluator. You have to reload your page each time you want to query a new value.
• Rhino is great for pure logic, but you can’t use it with anything that use a browser API. In fact, you can’t use it with anything that uses anything that uses a browser API. This means, for example, that you can’t use it with a library that uses Prototype, without writing some mock objects first.

One problem with JavaScript development is that the string representation of a value doesn’t tell you much about the value. For example, [null], [undefined], and '' all display as the empty string. [1,2}, [[1,2]], and [[1],[2]] all display as 1,2 (and so does "1,2"). And ({a: 1}), ({b: 2}), and new MySwankyNewObject() all display as [object Object].

If you use an IDE for development, this may not be a problem. Probably the IDE has its own string representation; even if it doesn’t, you can generally drill into objects by clicking on them. This doesn’t help those us of who prefer REPL development or printf-style debugging. When you display a debugging value (to the browser status line, to the alert() dialog, or to the Rhino console), you’d like some indication of what it actually is. And JavaScript doesn’t generally tell you, at least when the value is more complex than a string, number, or boolean.