intercept.js

small library to intercept a function from being called without modifying the function. or messing with your existing code.

• can be used set up mocks for tests var called = intercept(this, testFunction)
• or something like, if (unexpected_error) intercept(this, save_to_db, recover)
• or just intercepting stuff!

How to use

var called = intercept(context, function_to_intercept, listenerFunction)

function_to_intercept: The function to intercept. When this function is called, called will be populated and if there's a listenerFunction that will be notified. The next time function_to_intercept is called, it'll work as normal. (It intercepts once.)

context: The 'this' of function_to_intercept

called: (optional) false, will be populated with information when function_to_intercept is called

listenerFunction: (optional) will be called when function_to_intercept is called

Resetting

Given:

var called = intercept(context, function_to_intercept, listenerFunction)

called.reset();

Will reset an interception back to the original function. Useful only for when a function was never called and you want to reset it.

For all other cases intercept.js will auto reset.

Example

(for using it to setup mocks for tests)

// real function to mock / test
function Cat() {}
Cat.prototype.give = function(something) {
    if (something === 'catnip') throw new Error('CAT NIP!!!')
}

// start test
// setup intercept, result is 'false'
var result = intercept(Cat.prototype, Cat.prototype.give);

var cat = new Cat();

// call like normal, it gets intercepted, no error thrown
cat.give('catnip');

// result() is now populated
assert(result).is.eql({called: true, args: ['catnip'] })

// it resets your function back to normal
// so when called again, this will throw the error
cat.give();

// ( basically you don't have reset the mock or do anything else! )

Installing

Node:

npm install intercept.js

Browser:

Use the intercept.min.js file