Node.js Stream writable.end() Method

The writable.end() method is an inbuilt application programming interface of Stream module so that no more data can be written to the Writable anymore. The arguments chunk and encoding are optional which will permit one final new chunk of data to be written instantly before closing the stream. Moreover, the optional callback function is added as a listener for the ‘finish’ event of the Writable stream.

Syntax:

writable.end( chunk, encoding, callback)

Parameters: This method accepts three parameters as mentioned above and described below:

• chunk: It is an optional data to write. The value of chunk must be a string, buffer or Uint8Array. For object mode, the chunk value may be anything other than null.
• encoding: It holds the encoding value if chunk is a string value.
• callback: It is an optional callback function for stream.

Return Value: It returns the data written before calling this method and if the end() method has a chunk of new data then that is also returned at the end.

Below examples illustrate the use of writable.end() method in Node.js:

Example 1:

// Node.js program to demonstrate the
// writable.end() method

// INcluding stream module
const stream = require('stream');

// Creating a stream and creating
// a write function
const writable = new stream.Writable({

  // Write function with its
  // parameters
  write: function(chunk, encoding, next) {

    // Converting the chunk of
    // data to string
    console.log(chunk.toString());
    next();
  }
});

// Writing data
writable.write('hi');

// Calling end method with its
// all the parameters
writable.end("last data", "utf8", () => {
     console.log("Writable stream ended!");
});

Output:

hi
last data
Writable {
  _writableState:
   WritableState {
     objectMode: false,
     highWaterMark: 16384,
     finalCalled: false,
     needDrain: false,
     ending: true,
     ended: true,
     finished: false,
     destroyed: false,
     decodeStrings: true,
     defaultEncoding: 'utf8',
     length: 0,
     writing: false,
     corked: 0,
     sync: false,
     bufferProcessing: false,
     onwrite: [Function: bound onwrite],
     writecb: null,
     writelen: 0,
     bufferedRequest: null,
     lastBufferedRequest: null,
     pendingcb: 2,
     prefinished: true,
     errorEmitted: false,
     emitClose: true,
     autoDestroy: false,
     bufferedRequestCount: 0,
     corkedRequestsFree:
      { next: null,
        entry: null,
        finish: [Function: bound onCorkedFinish] } },
  writable: false,
  _write: [Function: write],
  domain: null,
  _events:
   [Object: null prototype] {
     finish: { [Function: bound onceWrapper] listener: [Function] } },
  _eventsCount: 1,
  _maxListeners: undefined }
Writable stream ended!

Example 2:

// Node.js program to demonstrate the
// writable.end() method

// INcluding stream module
const stream = require('stream');

// Creating a stream and creating
// a write function
const writable = new stream.Writable({

  // Write function with its
  // parameters
  write: function(chunk, encoding, next) {

    // Converting the chunk of
    // data to string
    console.log(chunk.toString());
    next();
  }
});

// Writing data
writable.write('hi');

// Calling end method with its
// all the parameters
writable.end("last data", "utf8", () => {
     console.log("Writable stream ended!");
});
writable.write('GfG');

Output:

hi
last data
Error [ERR_STREAM_WRITE_AFTER_END]: write after end
    at writeAfterEnd (_stream_writable.js:248:12)
    at Writable.write (_stream_writable.js:296:5)
    at /home/runner/LuxuriousLegitimateObservation/index.js:30:10
    at Script.runInContext (vm.js:133:20)
    at Object. (/run_dir/interp.js:156:20)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)Writab
le stream ended!

Here an error is displayed as write() method is called after end() method which is not possible.

Reference: https://nodejs.org/api/stream.html#stream_writable_end_chunk_encoding_callback