trough

trough

trough /trôf/ — a channel used to convey a liquid.

trough is like ware with less sugar, and middleware functions can change the input of the next.

Installation

npm:

npm install trough

Usage

var fs = require('fs');
var path = require('path');
var trough = require('trough');

var 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 (err, stats) {
      next(err, {filePath: filePath, stats: 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:21:12
    at wrapped (~/node_modules/trough/index.js:93:19)
    at next (~/node_modules/trough/index.js:56:24)
    at done (~/node_modules/trough/index.js:124:12)
    at ~/node_modules/example.js:14:7
    at FSReqWrap.oncomplete (fs.js:153:5)
null <Buffer 23 20 74 72 6f 75 67 68 20 5b 21 5b 42 75 69 6c 64 20 53 74 61 74 75 73 5d 5b 74 72 61 76 69 73 2d 62 61 64 67 65 5d 5d 5b 74 72 61 76 69 73 5d 20 5b ... >

API

trough()

Create a new Trough.

Trough

A pipeline.

Trough#run([input..., ]done)

Run the pipeline (all use()d middleware). Invokes done on completion with either an error or the output of the last middleware

Note! as the length of input defines whether async function get a next function, it’s recommended to keep input at one value normally.

function done(err?, [output...])

The final handler passed to run(), invoked 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 invoked with the output of its predecessor.

Synchronous

If fn returns or throws an error, the pipeline fails and done is invoked 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).

Example

The following example shows how returning an error stops the pipeline:

var trough = require('trough');

trough()
  .use(function (val) {
    return new Error('Got: ' + val);
  })
  .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:

var trough = require('trough');

trough()
  .use(function (val) {
    throw new Error('Got: ' + val);
  })
  .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:

var trough = require('trough');

trough()
  .use(function (val) {
    return 'even ' + val;
  })
  .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 invoked 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).

Example

The following example shows how rejecting a promise stops the pipeline:

var trough = require('trough');

trough()
  .use(function (val) {
    return new Promise(function (resolve, reject) {
      reject('Got: ' + val);
    });
  })
  .run('val', console.log);

Yields:

Got: val

The following example shows how the input isn’t touched by resolving to null.

var trough = require('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 invoked with that value.

If next is given no value (either null or undefined) as the first argument, all following non-nully values change the input of the following function, and all nully values default to the input.

Example

The following example shows how passing a first argument stops the pipeline:

var trough = require('trough');

trough()
  .use(function (val, next) {
    next(new Error('Got: ' + val));
  })
  .run('val', console.log);

Yields:

Error: Got: val
    at ~/example.js:5:10

The following example shows how more values than the input are passed.

var trough = require('trough');

trough()
  .use(function (val, next) {
    setTimeout(function () {
      next(null, null, 'values');
    }, 100);
  })
  .run('some', console.log);

Yields:

null 'some' 'values'

License

MIT © Titus Wormer