annotate

annotate.js - Asserts your function invariants

annotate.js allows you to attach certain metadata to your functions. For instance you could document invariants of your function this way. In addition you can attach an optional description you can access later on.

This metadata can be used by tools such as suite.js in order to generate tests. In addition you can access the metadata via REPL.

The usage is quite simple as the following example illustrates:

// let's define some function to annotate
function add(a, b) {
    return a + b;
}

// type checkers from is-js (https://npmjs.org/package/is-js)
var addNumbers = annotate('addNumbers', 'Adds numbers')
    .on(is.number, is.number, add);
var addStrings = annotate('addStrings', 'Adds strings')
    .on(is.string, is.string, add);

// you can assert invariants too
var addPositive = annotate('addPositive', 'Adds positive')
    .on(isPositive, isPositive, add)
    .satisfies(isPositive); // postcondition

// it is possible to chain guards
var fib = annotate('fib', 'Calculates Fibonacci numbers')
    .on(0, 0).on(1, 1)
    .on(is.number, function(n) {
        return fib(n - 1) + fib(n - 2);
    });

// invariants may depend on each other
var clamp = annotate('clamp', 'Clamps given number between given bounds')
    .on(is.number, is.number, function(a, args) {
        return is.number(a) && args[1] <= a;
    }, function(a, min, max) {
        return Math.max(Math.min(a, max), min);
    });

// furthermore it is possible to pass a variable amount of args
var min = annotate('min', 'Returns minimum of the given numbers')
    .on([is.number], Math.min);

function isPositive(a) {
    return a >= 0;
}

The annotate function will create a new function that contains the metadata as properties _name, _doc, _preconditions and _postconditions. In case some pre- or postcondition doesn't pass it won't return and gives a warning instead.

Related Projects

• suite.js - Constructs tests based on invariant data (fuzzing)
• funkit - Collection of utilities tested using annotate.js and suite.js

Acknowledgements

• Kris Jordan's multimethod.js - Provided inspiration for the API

License

annotate.js is available under MIT. See LICENSE for more details.