express-switch

express-switch

express-switch is a pattern matching middleware for express

Installation

$ npm install express-switch

Parameters

eSwitch(getter, pattern)

• getter (mandatory) a function that returns the value to match against the pattern
• pattern (mandatory) an object that describes the different routes to follow depending on the value returned by the getter

Getter

The getter is a function that is responsible to compute the value to match against the cases. This function can be synchronous or asynchronous.

Synchronous

The getter is synchronous when the number of parameters is less than 3. It has to return the value.

prototype

    function (req, res) { /* ... */ return value; }

example

var express = require('express');
var eSwitch = require('express-switch');
var app = express();
 
// ...
 
app.use(eSwitch(
    function(req, res){
        return value; // here you have to return the value to match against the cases
    },
    {
        case: {
            CASE1: middleware1, // this will be executed if the getter returns 'CASE1'
            CASE2: [middleware2, middleware3] // these will be execute if the getter returns 'CASE2'
        },
        default: middleware5 // this will be executed if the getter return neither 'CASE1' nor 'CASE2'
    }
));
 
// ...
 
app.listen(3000);

Asynchronous

The getter is asynchronous when the number of parameters is more than 2. It has to forward the value to the done callback.

prototype

    function (req, res, done) {
        // ...
        if (error) {
            done(undefined, error);
        } else {
            done(value);
        }
        // ...
    }

example

var express = require('express');
var eSwitch = require('express-switch');
var app = express();
 
// ...
 
app.use(eSwitch(
    function(req, res, done){
        something.doAsync(req, res, function(err, value){
            if (err){
                return done(undefined, err); // error forwarding
            }
            done(value); // you have to forward to the done callback the value to match against the cases
        });
    },
    {
        case: {
            CASE1: middleware1, // this will be executed if the getter returns 'CASE1'
            CASE2: [middleware2, middleware3] // these will be execute if the getter returns 'CASE2'
        },
        default: middleware5 // this will be executed if the getter return neither 'CASE1' nor 'CASE2'
    }
));
 
// ...
 
app.listen(3000);

Return an Array

If the getter returns/forwards an Array all the values will be analized sequencially, unless one of the middlewares forwards an error.

Pattern

The pattern is an object with the following properties.

• case (mandatory) a lookup table of middlewares or arrays of middlewares.
• default (optional) the default route to follow if none of the cases matches.

prototye

    var pattern = {
        case : {
            "value 1" : middleware1,
            "value 2" : [middleware2, middleware3],
            // ...
            "value N" : middleware
        },
        default : middleware // optional
    }