On type checking

More on type checking in JavaScript

(See also the "Comparison and inspiration" section for other JS type checking libraries.)

• There's a section about "Function Overloading and Type-Checking" that explains how to perform those task in the body of a function in John Resig's book "Pro JavaScript Techniques".
  • In particular, he proposes a method called "strict()" which checks an array of variables (e.g.: arguments) for proper constructors.
  • Google Books search-inside-the-book results here.
• Douglas Crockford's Remedial JavaScript, in particular the custom typeOf() function.
• Unifying JavaScript Argument-passing Styles: very recent (2008.08.25). Proposes a function (argumentative()) that wraps your function and allows you to check types and pass parameters with names instead of relying on order.
• typeOf() - A Way To Check Data Types: A custom JS function to retrieve the type of a variable.
• JavaScript's untyped function arguments, or: Try...Catch?: The author proposes to use try/catch blocks instead of explicit type checking, in some cases.

On "duck typing"

• From Wikipedia > Duck typing:
  • "duck typing is a style of dynamic typing in which an object's current set of methods and properties determines the valid semantics, rather than its inheritance from a particular class."
  • In the criticism section:
    • "duck typing [...] forces the programmer to have a much wider understanding of the code"
    • "you could easily create a class called Wine, which expects a class implementing the "press" attribute as an ingredient. However, a class called Trousers might also implement the press() method"
• From http://blog.michaeleee.com/2008/02/javascript-interfaces-and-duck-typing.html
  • "In summary, duck typing keeps things simple but requires you to trust your development team to keep track of all the details. Duck typing is popular among the Ruby community. As one moves from a small team to larger projects involving separate subgroups, you can not rely on this trust, and you may want to add a few checks and balances to your code on top of duck typing."
• http://www.sitepen.com/blog/2007/10/14/dealing-with-the-flexibility-of-javascript/

Best practices

• Python typecheck - best practices

Similar libraries in other dynamic languages

See also the "Comparison and inspiration" section, for other JavaScript code doing type checking.

• Python typecheck