ConfigurationObject

From APIDesign

Revision as of 10:50, 22 February 2015

ConfigurationObject pattern is often used by JavaScript libraries to deal with evolution in a manageable way. While TheAPIBook advocates getting ready for the fact that first version of any API is never perfect, people keep repeating the same design mistake again and again: optimistically ignore the need for evolution! Usual history of an API starts with introducing function with one argument:

function upper(text) {
  return text.toUpperCase();
}
upper("Hello World!") === "HELLO WORLD!" || error();

then one finds an additional argument is needed:

function upper(text, firstLetterOnly) {
  if (firstLetterOnly) {
    return text.substring(0, 1).toUpperCase() + text.substring(1);
  }
  return text.toUpperCase();
}
upper("hello world!") === "HELLO WORLD!" || error();
upper("hello world!", true) === "Hello world!" || error();

and later another one, and another and so on, until one realizes the whole API is total mess and it is time to switch to ConfigurationObject design pattern:

function upper(data, firstLetterOnly) {
  if (typeof data === "string") {
      data = {
          "text" : data,
          "firstLetterOnly" : firstLetterOnly
      };
  }
  if (data.firstLetterOnly) {
    return data.text.substring(0, 1).toUpperCase() + data.text.substring(1);
  }
  return data.text.toUpperCase();
}
upper({ 
  "text" : "hello world!"
}) === "HELLO WORLD!" || error();
upper({ 
  "text" : "hello world!",
  "firstLetterOnly" : false
}) === "HELLO WORLD!" || error();
upper({ 
  "text" : "hello world!",
  "firstLetterOnly" : true
}) === "Hello world!" || error();

Adding named parameters is more easily evolvable. Moreover it is certainly easier to use ten named arguments than a function with ten parameters. No surprise the ConfigurationObject becomes more and more popular in many JavaScript libraries.

Now let's take a Java view. DukeScript (a way to use HTML from Java) is all about Java and JavaScript co-operation. To prevent reinventing the wheel the core of DukeScript ecosystem is built around wrapping JavaScript libraries with type-safe Java APIs. As ConfigurationObject is becoming more frequent, it is more and more important to find proper realization of such API in Java. Let's discuss the options.

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