https://github.com/commenthol/connect-chain-if
Compose a new middleware from a chain of middlewares to be called in series
https://github.com/commenthol/connect-chain-if
Last synced: about 1 month ago
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Compose a new middleware from a chain of middlewares to be called in series
- Host: GitHub
- URL: https://github.com/commenthol/connect-chain-if
- Owner: commenthol
- License: mit
- Created: 2014-06-18T06:29:29.000Z (about 12 years ago)
- Default Branch: master
- Last Pushed: 2022-11-12T11:46:57.000Z (over 3 years ago)
- Last Synced: 2025-10-20T17:48:31.599Z (8 months ago)
- Language: JavaScript
- Homepage:
- Size: 32.2 KB
- Stars: 2
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Connect-Chain-If
"connect-chain-if" is a middleware that composes a new middleware of type `function(req, res, next)` from a chain of middlewares to be called in series.
The new middleware is fully [connect][connect] compliant.
An error passed to `next` or thrown in a middleware will short circuit the chain and be
passed to the next error middleware of type `function(err, req, res, next)` in the connect middleware chain.
You can use "connect-chain-if" to build up new middlewares from existing connect-style-middlewares using the conditional expressions `chain.if()` and `chain.switch()`.
To allow breaking up long lasting middleware chains, all middlewares within a chain are processed via the node event loop using `process.nextTick` instead of being processed synchroniously. Use `chain.nextTick(false);` to revert to the synchronous behaviour.
## Usage
### Building new middlewares
```javascript
var
express = require('express'),
chain = require('connect-chain-if');
var
app = express(),
middleware1 = function(req, res, next) {
res.body = req.url + '\n';
next && next();
},
middleware2 = function(req, res, next) {
res.writeHead(200);
res.write(res.body || '');
res.end();
next && next();
};
var newMiddleware = chain([ middleware1, middleware2 ]);
// or to maintain backward compatibility
newMiddleware = chain(middleware1, middleware2);
// then use it in express/ connect
app.use(newMiddleware);
app.listen(3000);
```
### Building middlewares with error traps
```javascript
var
chain = require('connect-chain-if');
var
middleware1 = function(req, res, next) {
// ... something bad happened
console.log('middleware1');
next && next(new Error('error'));
},
middleware2 = function(req, res, next) {
console.log('middleware2');
next && next();
},
middleware3 = function(req, res, next) {
console.log('middleware3');
next && next();
},
middlewareErr = function(err, req, res, next) { // note the "4" arguments
console.log('trapped error:', err.message);
next && next();
};
next && next();
};
chain([
middleware1,
middleware2,
middlewareErr,
middleware3
])({},{});
```
In this example `middleware2` will be bypassed. Output is:
```
middleware1
trapped error: error
middleware3
```
### Using connect middlewares without connect/ express
```javascript
var
http = require('http'),
chain = require('connect-chain-if');
var
middleware1 = function(req, res, next) {
if (/^\/[a-z]?$/.test(req.url)) {
res.body = req.url;
next && next();
}
else {
next && next(new Error('err'));
}
},
middleware2 = function(req, res, next) {
res.writeHead(200);
res.write(res.body || '');
res.end();
},
middlewareErr = function(err, req, res, next) {
res.writeHead(404);
res.end();
};
http.createServer(chain(middleware1, middleware2, middlewareErr))
.listen(3000, 'localhost');
```
*NOTE:* Take care that in this case your very last middleware in the `chain` handles any error.
```bash
curl -v localhost:3000/a
#> < HTTP/1.1 200 OK
#> /a
curl -v localhost:3000/aaa
#> < HTTP/1.1 404 Not Found
```
### Creating conditional middlewares
You can either use `chain.if` or `chain.switch` to define conditional middlewares.
```javascript
var
chain = require('connect-chain-if');
var middleware = function(req, res, next) {
chain([
chain.if(
/*if */ /^\/$/.test(req.url), [ // defines a new middleware chain here
function(req, res, next) {
res.body = 'homepage';
next && next();
},
function(req, res, next) {
res.statusCode = 200;
next && next();
}],
/*if */ /^\/error500$/.test(req.url), function(req, res, next) {
res.body = 'weired';
res.statusCode = 500;
next && next();
},
/*else */ function(req, res, next) {
res.body = 'no idea';
res.statusCode = 404;
next && next();
}
),
function (req, res, next) {
console.log(res.statusCode, res.body);
next && next();
}
])(req, res, function (err) {
next && next(err);
});
};
middleware({ url: '/' }, {});
//> 200 'homepage'
middleware({ url: '/error500'}, {});
//> 500 'weired'
middleware({ url: '/something'}, {});
//> 404 'no idea'
```
Using `chain.switch`:
```javascript
var
chain = require('connect-chain-if');
var middleware = function(req, res, next) {
chain([
chain.switch(
/*switch */ req.url,
/*case */ '/', [ // defines a new middleware chain here
function(req, res, next) {
res.body = 'homepage';
next && next();
},
function(req, res, next) {
res.statusCode = 200;
next && next();
}],
/*case */ '/error500', function(req, res, next) {
res.body = 'weired';
res.statusCode = 500;
next && next();
},
/*default */ function(req, res, next) {
res.body = 'no idea';
res.statusCode = 404;
next && next();
}
),
function (req, res, next) {
console.log(res.statusCode, res.body);
next && next();
}
])(req, res, function (err) {
next && next(err);
});
};
middleware({ url: '/' }, {});
//> 200 'homepage'
middleware({ url: '/error500'}, {});
//> 500 'weired'
middleware({ url: '/something'}, {});
//> 404 'no idea'
```
## License
Software is released under [MIT][license].
[connect]: https://github.com/senchalabs/connect
[license]: ./LICENSE