toMethod and toLambda - higher order helpers for codebases that use both functional and OOP styles

tomethod-toLambda.js

// Convert a function that does not use `this` context into a function that
// does. The category of information that was previously passed as the first
// parameter of the function is now its `this` context.
function toMethod(lambda) {
  return function () {
    var args = [this];
    var concat = args.concat;
    // Spread arguments over arity of concat, since arguments is not a true array.
    var combined = concat.apply(args, arguments);
    return lambda.apply(null, combined);
  };
}

// Convert a method func that uses a `this` context into a function that takes
// the context object as the first parameter.
function toLambda(method) {
  return function (context) {
    var args = Array.prototype.slice.call(arguments, 1);
    return method.apply(context, args);
  };
}

Also note that if a bound function is passed to toFunction, the resulting function will throw away the first argument when called. No way around that, but one can assume that functions which bind this know their own implementation and can fend for themselves.

We actually use on of this functions in SDK :)
https://github.com/mozilla/addon-sdk/blob/master/packages/api-utils/lib/functional.js#L18-23

I like the use of the term "lambda" in your example to distinguish between methods and traditional functions. Maybe toLambda and toMethod are better names?

Update: changed the name to Lambda.