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Express param pre-condition functions

branch: master
Readme.md

express-params

Express param pre-condition functions.

Installation

Works with Express 2.5.x

$ npm install express-params

Usage

Simply invoke the extend() method on an express HTTPServer to add this functionality.

var express = require('express')
  , params = require('express-params')
  , app = express.createServer();

params.extend(app);

RegExp

Regular expressions can be used to extract data from pathname segments as shown below. When matched req.params.range contains the capture groups of the regexp.exec() call.

app.param('range', /^(\w+)\.\.(\w+)?$/);

app.get('/range/:range', function(req, res, next){
  var range = req.params.range;
  res.send('from ' + range[1] + ' to ' + range[2]);
});

Another use-case for regular expression parameters is to validate input, for example here we may want to route via numeric id, followed by a route which will accept other values.

app.param('uid', /^[0-9]+$/);

app.get('/user/:uid', function(req, res, next){
  var uid = req.params.uid;
  res.send('user ' + uid);
});

app.get('/user/:name', function(req, res, next){
  var name = req.params.name;
  res.send('user ' + name);
});

Return Value

Functions with arity < 3 (less than three parameters) are not considered to be middleware-style, and are useful for type coercion. For example below we pass Number, a function which accepts a string coercing to a number, alternatively we could use parseInt here. The result of req.params.id will then be a number, however if we were to issue GET /user/tj the result would be NaN, which is considered invalid by exports.invalidParamReturnValue(val) so next('route') is called, ignoring the route.

app.param('id', Number);

app.get('/user/:id', function(req, res, next){
  var id = req.params.id;
  res.send('typeof ' + typeof id + ' ' + id);
});

The following default logic is applied to test if a return value is invalid:

return null == val
  || false === val
  || ('number' == typeof val && isNaN(val));

It's safe to throw in these functions, as connect's router wraps them in a try/catch block, and they are not asynchronous.

Running Tests

First install dependencies:

 $ npm install -g

Then run the tests:

 $ make test

License

(The MIT License)

Copyright (c) 2011 TJ Holowaychuk <tj@vision-media.ca>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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