Introduction to map-stream

map-stream is a powerful Node.js module designed for working with streams. It allows you to easily transform data as it passes through the stream pipelines. This makes it particularly useful for handling large datasets, performing real-time data processing, and more.

Core APIs of map-stream

Basic Usage

The map-stream module can be easily included in your Node.js project:

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

Simple Mapping

Transforming a stream of data is straightforward with the map function. Below is a basic example:

  const through = require('through');
  const map = require('map-stream');

  const stream = through();
  const mapStream = stream.pipe(map((data, callback) => {
    data = data.toString().toUpperCase();
    callback(null, data);
  }));

  mapStream.on('data', (data) => {
    console.log(data);
  });

  stream.write('hello');
  stream.end();

Filtering Data

You can also filter data within streams with map-stream:

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

  const filterStream = map((data, callback) => {
    const number = parseInt(data.toString(), 10);
    if (number % 2 === 0) {
      callback(null, data);
    } else {
      callback();
    }
  });

  someInputStream.pipe(filterStream).pipe(process.stdout);

Error Handling

Handling errors within a stream is also supported:

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

  const errorStream = map((data, callback) => {
    if (data.toString().includes('error')) {
      callback(new Error('Stream contains error'));
    } else {
      callback(null, data);
    }
  });

  errorStream.on('error', (err) => {
    console.error('Error:', err.message);
  });

  someInputStream.pipe(errorStream).pipe(process.stdout);

Practical Application Example

Below is a practical application example where we combine different functionalities of map-stream:

  const map = require('map-stream');
  const through = require('through');

  const appStream = through();
  const upperCaseStream = map((data, callback) => {
    callback(null, data.toString().toUpperCase());
  });
  const filterEvenStream = map((data, callback) => {
    const number = parseInt(data.toString(), 10);
    if (number % 2 === 0) {
      callback(null, data);
    } else {
      callback();
    }
  });

  appStream.pipe(upperCaseStream).pipe(filterEvenStream).pipe(process.stdout);

  appStream.write('1');
  appStream.write('2');
  appStream.write('3');
  appStream.write('4');
  appStream.end();

Conclusion

map-stream is an excellent module for handling stream transformations in Node.js. Its simplicity and versatility enable you to build robust and efficient data-processing pipelines with ease. Happy coding!

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