filter.js

An approach to aspect-oriented programming (AOP) in javascript for both node.js and browser.

There are different use cases where AOP comes in handy, cases like logging, caching, testing, debugging, before/after filters and so on. filter.js provides an elegant approach to AOP in javascript.

Installation
----------

npm install filter.js

How to use
----------

`` javascript
Filter = require('filter.js');

// Every call to object.method will be wrapped by our filter
// Multiple filters can be applied to a single method
var f = new Filter(object, 'method', function(args, next) {
// do something with the args
var result = next(args);
// do something with the result
return result;
});

// Temporary disable filter
f.off();

// Activate a disabled filter
f.on();

// Premanently remove filter
f.remove();
`

Here is an example usage of filter.js to log and cache mysql queries:

` javascript
var Filter = require('filter.js');
var mysql = require('mysql');
var connection = mysql.createConnection({
host : 'localhost',
user : 'user',
password : 'secret',
database : 'mydb'
});
var cache = {};

//Log queries
new Filter(connection, 'query', function(args, next) {
var query = args[0];
var callback = args[1];
var start = Date.now();

args[1] = function(err, rows) {
console.log(query);
console.log('Took ' + (Date.now() - start) + ' ms');
callback(err, rows);
};

return next(args);
});

// Cache SELECT queries
new Filter(connection, 'query', function(args, next) {
var query = args[0];
var callback = args[1];

// Cache only SELECT queries
if (!query.match(/^SELECT/i)) {
return next(args);
}

//Check if we already have cached result in memory
if (cache[query]) {
// skip executing the query
callback(null, cache[query]);
return;
}

args[1] = function(err, rows) {
cache[query] = rows;
callback(err, rows);
};

return next(args);
});


connection.query('SELECT * FROM posts', function(err, rows) {
console.log(rows);
});
``

License
-------
filter.js is released under the MIT license.

The idea is inspired by li3 filter system.