.. | ||
index.d.ts | ||
index.js | ||
license | ||
package.json | ||
readme.md |
trough
trough
is middleware.
Contents
- What is this?
- When should I use this?
- Install
- Use
- API
- Types
- Compatibility
- Security
- Contribute
- License
What is this?
trough
is like ware
with less sugar.
Middleware functions can also change the input of the next.
The word trough (/trôf/
) means a channel used to convey a liquid.
When should I use this?
You can use this package when you’re building something that accepts “plugins”, which are functions, that can be sync or async, promises or callbacks.
Install
This package is ESM only. In Node.js (version 12.20+, 14.14+, or 16.0+), install with npm:
npm install trough
In Deno with esm.sh
:
import {trough} from "https://esm.sh/trough@2"
In browsers with esm.sh
:
<script type="module">
import {trough} from "https://esm.sh/trough@2?bundle"
</script>
Use
import process from 'node:process'
import fs from 'node:fs'
import path from 'node:path'
import {trough} from 'trough'
const pipeline = trough()
.use(function (fileName) {
console.log('Checking… ' + fileName)
})
.use(function (fileName) {
return path.join(process.cwd(), fileName)
})
.use(function (filePath, next) {
fs.stat(filePath, function (error, stats) {
next(error, {filePath, stats})
})
})
.use(function (ctx, next) {
if (ctx.stats.isFile()) {
fs.readFile(ctx.filePath, next)
} else {
next(new Error('Expected file'))
}
})
pipeline.run('readme.md', console.log)
pipeline.run('node_modules', console.log)
Yields:
Checking… readme.md
Checking… node_modules
Error: Expected file
at ~/example.js:22:12
at wrapped (~/node_modules/trough/index.js:111:16)
at next (~/node_modules/trough/index.js:62:23)
at done (~/node_modules/trough/index.js:145:7)
at ~/example.js:15:7
at FSReqCallback.oncomplete (node:fs:199:5)
null <Buffer 23 20 74 72 6f 75 67 68 0a 0a 5b 21 5b 42 75 69 6c 64 5d 5b 62 75 69 6c 64 2d 62 61 64 67 65 5d 5d 5b 62 75 69 6c 64 5d 0a 5b 21 5b 43 6f 76 65 72 61 ... 7994 more bytes>
API
This package exports the identifiers trough
and wrap
.
There is no default export.
trough()
Create a new Trough
.
wrap(middleware, callback)(…input)
Call middleware
with all input.
If middleware
accepts more arguments than given in input, an extra done
function is passed in after the input when calling it.
In that case, done
must be called.
The first value in input
is the main input value.
All other input values are the rest input values.
The values given to callback
are the input values, merged with every
non-nullish output value.
- If
middleware
throws an error, returns a promise that is rejected, or calls the givendone
function with an error,callback
is called with that error - If
middleware
returns a value or returns a promise that is resolved, that value is the main output value - If
middleware
callsdone
, all non-nullish values except for the first one (the error) overwrite the output values
Trough
A pipeline.
Trough#run([input…, ]done)
Run the pipeline (all use()
d middleware).
Calls done
on completion with either an error or the output of the
last middleware.
👉 Note: as the length of input defines whether async functions get a
next
function, it’s recommended to keepinput
at one value normally.
function done(err?, [output…])
The final handler passed to run()
, called with an error if a
middleware function rejected, passed, or threw one, or the output of the
last middleware function.
Trough#use(fn)
Add fn
, a middleware function, to the pipeline.
function fn([input…, ][next])
A middleware function called with the output of its predecessor.
Synchronous
If fn
returns or throws an error, the pipeline fails and done
is called
with that error.
If fn
returns a value (neither null
nor undefined
), the first input
of
the next function is set to that value (all other input
is passed through).
The following example shows how returning an error stops the pipeline:
import {trough} from 'trough'
trough()
.use(function (thing) {
return new Error('Got: ' + thing)
})
.run('some value', console.log)
Yields:
Error: Got: some value
at ~/example.js:5:12
…
The following example shows how throwing an error stops the pipeline:
import {trough} from 'trough'
trough()
.use(function (thing) {
throw new Error('Got: ' + thing)
})
.run('more value', console.log)
Yields:
Error: Got: more value
at ~/example.js:5:11
…
The following example shows how the first output can be modified:
import {trough} from 'trough'
trough()
.use(function (thing) {
return 'even ' + thing
})
.run('more value', 'untouched', console.log)
Yields:
null 'even more value' 'untouched'
Promise
If fn
returns a promise, and that promise rejects, the pipeline fails and
done
is called with the rejected value.
If fn
returns a promise, and that promise resolves with a value (neither
null
nor undefined
), the first input
of the next function is set to that
value (all other input
is passed through).
The following example shows how rejecting a promise stops the pipeline:
import {trough} from 'trough'
trough()
.use(function (thing) {
return new Promise(function (resolve, reject) {
reject('Got: ' + thing)
})
})
.run('thing', console.log)
Yields:
Got: thing
The following example shows how the input isn’t touched by resolving to null
.
import {trough} from 'trough'
trough()
.use(function () {
return new Promise(function (resolve) {
setTimeout(function () {
resolve(null)
}, 100)
})
})
.run('Input', console.log)
Yields:
null 'Input'
Asynchronous
If fn
accepts one more argument than the given input
, a next
function is
given (after the input). next
must be called, but doesn’t have to be called
async.
If next
is given a value (neither null
nor undefined
) as its first
argument, the pipeline fails and done
is called with that value.
If next
is given no value (either null
or undefined
) as the first
argument, all following non-nullish values change the input of the following
function, and all nullish values default to the input
.
The following example shows how passing a first argument stops the pipeline:
import {trough} from 'trough'
trough()
.use(function (thing, next) {
next(new Error('Got: ' + thing))
})
.run('thing', console.log)
Yields:
Error: Got: thing
at ~/example.js:5:10
The following example shows how more values than the input are passed.
import {trough} from 'trough'
trough()
.use(function (thing, next) {
setTimeout(function () {
next(null, null, 'values')
}, 100)
})
.run('some', console.log)
Yields:
null 'some' 'values'
Types
This package is fully typed with TypeScript.
Compatibility
This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, and 16.0+. It also works in Deno and modern browsers.
Security
This package is safe.
Contribute
Yes please! See How to Contribute to Open Source.