README

function-filter

Simple AOP using filterable function wrappers

What is function-filter?

function-filter is an efficient and lightweight way to allow logic to be extended across different concerns of your application. By wrapping a function in a filter, it is possible to dynamically intercept and optionally modify parameter and return values to the underlying function.

In addition, filters can call alternative logic, or nothing at all, depending on the use case.

Some examples of why you may want to do this include:

Logging the parameters passed to a critical function before it is called, and the returned value afterwards.
Mutating queries to a database resource, to enforce security constraints.
Mutating query results, to redact private information.
Memoizing expensive functions based on their input parameters.

Installation

npm install function-filter

Usage

Usage under ES5 and ES6 is essentially the same:

ES5:

var filter = require('function-filter').default;
var myFn = filter(function(chain, argA, argB) {
    console.log(argA, argB);
});

myFn("Hello", "World!");
// Hello World!

myFn.addFilter(function(chain, argA, argB) {
    console.log("Originally called with:", argA, argB);
    return chain.next(chain, "Goodbye", argB);
});

myFn("Hello", "World!");
// Originally called with Hello World!
// Goodbye World!

ES6:

import filter from 'function-filter';
const myFn = filter((chain, argA, argB) => {
    console.log(argA, argB);
});

myFn("Hello", "World!");
// Hello World!

myFn.addFilter((chain, argA, argB) => {
    console.log("Originally called with:", argA, argB);
    return chain.next(chain, "Goodbye", argB);
});

myFn("Hello", "World!");
// Originally called with Hello World!
// Goodbye World!

Changelog

This project adheres to Semantic Versioning. For a list of detailed changes, please refer to CHANGELOG.md.

Contributing

Please see CONTRIBUTING.md.

Prior Art

This implementation is heavily inspired by li3's filter system.

License

function-filter is released under the BSD 3-clause “New” License.

Usage no npm install needed!