The map-stream npm package is a simple stream transformation tool that allows you to create a through stream from an asynchronous function. It is primarily used for applying a function to every item in a stream, effectively enabling transformation and processing of stream data in an easy and flexible manner.

What are map-stream's main functionalities?

Asynchronous Transformation

This feature allows for the asynchronous transformation of stream data. The provided code sample reads data from 'input.txt', transforms it to uppercase asynchronously, and writes the transformed data to 'output.txt'.

var map = require('map-stream');
var fs = require('fs');

var inputStream = fs.createReadStream('input.txt');
var outputStream = fs.createWriteStream('output.txt');

var transformStream = map(function(data, callback) {
  // Asynchronously transform data
  var transformedData = data.toString().toUpperCase();
  callback(null, transformedData);
});

inputStream.pipe(transformStream).pipe(outputStream);

Error Handling

This feature demonstrates how to handle errors within the map-stream. If the data contains the string 'error', an error is passed to the callback, which is then handled by listening to the 'error' event on the stream.

var map = require('map-stream');

var transformStream = map(function(data, callback) {
  // Simulate an error under certain condition
  if(data.toString().includes('error')) {
    callback(new Error('Error found in data'));
  } else {
    callback(null, data);
  }
});

transformStream.on('error', function(err) {
  console.error('Error:', err.message);
});

Other packages similar to map-stream

Readme

Source

MapStream

Refactored out of event-stream

##map (asyncFunction[, options])

Create a through stream from an asyncronous function.

var map = require('map-stream')

map(function (data, callback) {
  //transform data
  // ...
  callback(null, data)
})

Each map MUST call the callback. It may callback with data, with an error or with no arguments,

callback() drop this data.
this makes the map work like filter,
note:callback(null,null) is not the same, and will emit null
callback(null, newData) turn data into newData
callback(error) emit an error for this item.

Note: if a callback is not called, map will think that it is still being processed,
every call must be answered or the stream will not know when to end.

Also, if the callback is called more than once, every call but the first will be ignored.

##Options

failures - boolean continue mapping even if error occured. On error map-stream will emit failure event. (default: false)

FAQs

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Last updated on 19 Mar 2017

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