contracts ^link

A small library to cleanly implement design by contract.

Status: beta

Motivation :

var f = function(a, b) {
	return a + b;
}

var f = f.pre(function(a, b) {
	a.should.be.a("number").and.above(0);
	b.should.be.a("number").and.above(0);
}).post(function(ret, a, b) {
	ret.should.be.equal(a + b);
});

It is recommended you only use contracts as part of unit tests or in development. contracts run at run-time and therefore negatively impact run-time performance.

Examples: ^link

See the examples folder

Documentation: ^link

See the annotated source code

Method invocation: ^link

The contract methods can be invoked in three different ways.

• f = f.pre(pre_cb);
• f = contract(f).pre(pre_cb).valueOf();
• f = contract.pre(pre_cb, f);

contract ^link

options is hash that can be passed various values:

• "natives" : default is true, if true it will extend Function.prototype

  var contract = require("contract")(options)

contract.pre ^link

pre allows you to assign a pre contract. Here you can assert that the arguments the function is invoked with should pass certain conditions.

The pre contract will be invoked before the function is invoked.

f = contract.pre(function(arg1, arg2, arg3, ...) {
    // assert things about the arguments
}, f)

contract.post ^link

post allows you to assign a post contract. Here you can assert that the return value matches certain conditions.

The post contract will be invoked after the function is invoked

f = contract.post(function(retValue, arg1, arg2, arg3, ...) {
    // assert things about the return value
}, f);

contract.invariant ^link

invariant allows you to assign a invariant contract. Here you can assert that there are no unexpected side effects during the function call.

The invariant contract will be invoked after the function is invoked

o.f = contract.invariant(function(before, arg1, arg2, arg3, ...) {
    // `before` is the state of `this` before the function was called
    // `this` is the current state of `this`
});