Express Response Hooks
Extend Express.js with response hooks, primarily aimed to manipulate the response before being sent to the client.
Installation
npm install express-response-hooks
Usage
const responseHooks = require('express-response-hooks');
// response hooks initialization
app.use(responseHooks());
// register a middleware that adds a "Cache-Control" header whenever the status code changes
app.use(function (req, res, next) {
// hook on "statusCode" changes
res.hooks.on('statusCode', ([ statusCode ]) => {
if (req.method.toUpperCase() === 'GET') && (statusCode < 400)) {
res.set('Cache-Control', 'public, max-age=5, s-maxage=31536000');
}
});
);
API
require('express-response-hooks')([options])
Creates a middleware that adds hooks to the response object
Options object
-
plugName- Type:
string - Default:
"hooks"
Controls under which key the hooks event emitter will be available in the response object. Default to
res.hooks - Type:
res.hooks
The hooks EventEmitter that enables registration to the following events:
| Event Name | Trigger | Arguments Array | Trigger |
|---|---|---|---|
| "statusCode" | res.statusCode |
status code (int) | statusCode property is changed internally |
| "set" | res.set() |
header name (string), header value (string) | set() is called internally or explicitly |
| "send" | res.send() |
body (int / object / string) | send() is called internally (e.g., res.json() calls it twice) or explicitly |
For example
res.hooks.once('statusCode', ([ statusCode ]) => {
// called once when the res.statusCode is changed for the first time
});
res.hooks.on('res', ([ name, value ]) => {
// called whenever res.res() is called internally by express to set default headers or explicitly
});
Data manipulation
Changing the values in the arguments array will change the arguments passed to the original wrapped property/function
For example
res.hooks.on('res', (args) => {
const [ name, value ] = args;
if (name === 'cache-control') {
// change the value of the header
args[1] = args[1].replace('public', 'private');
}
});
res.hooks.bypass
An object with references to the wrapped properties and functions for using them without triggering an event.
For example
res.hooks.on('set', ([ name, value ]) => {
if (name === 'cache-control') {
// add additional header without triggering another 'set' event
res.hooks.bypass.set('cdn-cache-control', value);
}
});
Notice
- You should take into consideration that Express internally calls some of the response functions right before the response gets sent to the client (e.g., adding default headers)
statusCodemanipulation will not work if the hook was triggered bysend()
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