readable.push(chunk[, encoding]) function in Node.js

The push(chunk[, encoding]) function of readable in Node.js is one of the integral functions pertaining to the Streams API for handling readable streams. Streams in Node.js allows developers to handle large data inputs efficiently by breaking them into easier-to-manage chunks, thereby providing a more effective, asynchronous, and memory-efficient way of handling data. The push method within readable streams is important to control the sending of data in a stream, be it based upon an event or custom logic.

Understanding Node.js Streams

In order to understand the usability of readable.push(chunk[, encoding]) function, it's helpful to have a general idea of Node.js streams. Streams are objects that enable reading and writing data in continuous flows, usually in chunks rather than all at once. It is especially practical for working with huge data sources like files, network requests, or database queries that would be too large to handle comfortably in memory if they were loaded in one go.

In Node.js, streams are divided into four major categories:

• Readable: Streams from which data can be read (for example, reading a file).
• Writable: Streams to which data can be written (for example, writing to a file).
• Duplex: Streams that are readable and writable (for example, a socket).
• Transform: Duplex streams modify or transform the data as it's being read or written (for example, a file compression stream).

Readable Stream and readable.push(chunk[, encoding])

The readable.push(chunk[, encoding]) method is used manually to push data chunks into the read queue of a readable stream. It proves very common when implementing custom readable streams, where you want to precisely decide when and how data is available for consumers of the stream.

The push method works thus:

• Chunk: The data to push in the read queue of the stream. The chunk can be Buffer, a string, or null.
• Encoding (optional): It is an encoding for a chunk if it's a string (like 'utf8', 'ascii', etc.). In case the chunk is a Buffer, or the stream is in object mode, this parameter is ignored.

The push function evaluates to true or false, which indicates that the high-water mark of the stream's Buffer has been exceeded. If the push returns false, you know that the internal Buffer is full and should not push further data into it until it is drained; thus, you save memory.

Key Points about readable.push(chunk[, encoding]):

Several key points about readable.push() function in Node.js are as follows:

• Manual Control: The push allows developers to control when and how their data enters the readable stream, which is useful in custom stream implementations.
• Buffer Management: By observing the return value of push, you can monitor the stream's Buffer and avoid excessive memory usage.
• Object Mode: If the stream is an object mode (meaning it has been set up to accommodate non-string, non-buffer objects), you can push any JavaScript object into it without an encoding.
• End of Data: Pushing null into the stream signals the end of data, after which no further data will be consumed from the stream.

Example of Using readable.push(chunk[, encoding])

Let us take an example to illustrate the readable.push(chunk[, encoding]) function in Node.js. This readable stream will manually generate its data by pushing a fixed number of chunks into it and signal completion by pushing null.

Output:

Explanation:

In this example:

• The CustomReadableStream class extends Readable and implements the _read() method. The _read method is required when implementing custom readable streams.
• In each call to _read, we push a new chunk of data until we reach maxChunks. Once this limit is reached, push(null) is called to signal the end of the stream.
• The data event on customStream handles each chunk as it's pushed into the readable stream.

Practical Use Cases of readable.push(chunk[, encoding])

Several practical use cases of the readable.push() function in Node.js are as follows:

• API or Database Data Streams: While fetching data through an API or database, the developer might prefer pushing every response or batch of data as it arrives. It is useful when you don't know the size of the data beforehand or if it's generated or fetched dynamically.
• Simulating Real-Time Data: In real-time applications like chat apps or live dashboards, data may be generated as a response to events in real time. Use the push function to add those events to the readable stream that provides a very efficient way of processing real-time data.
• File Processing: When a file is read line-by-line or chunk-by-chunk, pushing each line or chunk as it is read provides fine-grained control over memory usage and processing flow.
• Object Streams: For non-buffer, non-string data, object streams are useful for working with JavaScript objects.