javascript - Creating Transform stream using ExcelJS for writing xlsx -

i'm using exceljs module , writing wrapper purposes, implements transform stream api (yes, node version 0.10.40).

exceljs has stream api , according example in exceljs module can use 1 (execute node index.js > test.xlsx):

var stream = require('stream'),     excel = require('exceljs');  var rs = new stream.readable({objectmode: true}); rs.push({name: 'one'}); rs.push({name: 'two'}); rs.push({name: 'three'}); rs.push(null);  var workbook = new excel.stream.xlsx.workbookwriter({stream: process.stdout}),     worksheet = workbook.addworksheet('sheet 1');  worksheet.columns = [{header: 'name', key: 'name'}];  rs.on('data', function(doc) {     worksheet.addrow({         name: doc.name     }).commit(); });  rs.on('end', function(doc) {     worksheet.commit();     workbook.commit(); }); 

and working fine, looks not clean. because cannot use .pipe.

what need:

'use strict';  var buffer = require('buffer'),     stream = require('stream'),     util = require('util'),     excel = require('exceljs');  var rs = new stream.readable({objectmode: true}); rs.push({name: 'one'}); rs.push({name: 'two'}); rs.push({name: 'three'}); rs.push(null);  var exceltransform = function(options) {     stream.transform.call(this, options);     this._writablestate.objectmode = true;     this._readablestate.objectmode = false;      this.workbook = new excel.stream.xlsx.workbookwriter({stream: this});     this.worksheet = this.workbook.addworksheet('sheet 1');     this.worksheet.columns = [{header: 'name', key: 'name'}]; };  util.inherits(exceltransform, stream.transform);  exceltransform.prototype._transform = function(chunk, encoding, callback) {     if (buffer.buffer.isbuffer(chunk)) {         this.push(chunk);     } else {         this.worksheet.addrow({             name: chunk.name         }).commit();     }     callback(); };  exceltransform.prototype._flush = function(callback) {     this.worksheet.commit();     this.workbook.commit();     callback(); };  rs.pipe(new exceltransform()).pipe(process.stdout); 

but not working , giving me empty output.

the output empty because you're pushing nothing out of transform stream. you're in object mode never goes in if:

if (buffer.buffer.isbuffer(chunk)) {   this.push(chunk); } 

here working pipeable version (the data streamed @ once @ end):

var stream = require('stream'); var util = require('util'); var excel = require('exceljs'); var bl = require('bl');  var exceltransform = function(options) {   stream.transform.call(this, { objectmode: true });    this.workbook = options.workbook;   // can make optional checking ,   // creating empty worksheet if none provided   this.worksheet = options.worksheet; }  util.inherits(exceltransform, stream.transform);  exceltransform.prototype._transform = function(doc, encoding, callback) {   this.worksheet.addrow({ name: doc.name });       callback(); };  exceltransform.prototype._flush = function(callback) {   this.workbook.commit(); // commit when you're done    var = this;   // bl drains stream , create buffer object can push   this.workbook.stream.pipe(bl(function(err, data) {     that.push(data);     callback();   })); };  // it's better provide workbook parameter exceltransform var workbook = new excel.stream.xlsx.workbookwriter(); var worksheet = workbook.addworksheet('sheet 1'); worksheet.columns = [{   header: 'name',   key: 'name' }];  var rs = new stream.readable({ objectmode: true }); rs.push({ name: 'one' }); rs.push({ name: 'two' }); rs.push({ name: 'three' }); rs.push(null);  rs.pipe(new exceltransform({   workbook: workbook,   worksheet: worksheet })).pipe(process.stdout); 

another solution, streaming time:

var stream = require('stream'); var util = require('util'); var excel = require('exceljs');  var exceltransform = function(options) {   stream.transform.call(this, {     writableobjectmode: true,     readableobjectmode: false   });    this.workbook = options.workbook;   var = this;   this.workbook.stream.on('readable', function() {     var chunk = workbook.stream.read();     that.push(chunk);   });   this.worksheet = options.worksheet; }  util.inherits(exceltransform, stream.transform);  exceltransform.prototype._transform = function(doc, encoding, callback) {   this.worksheet.addrow({     name: doc.name   }).commit();    callback(); };  exceltransform.prototype._flush = function(callback) {   this.workbook.commit(); // final commit };  // it's better provide workbook parameter exceltransform var workbook = new excel.stream.xlsx.workbookwriter(); var worksheet = workbook.addworksheet('sheet 1'); worksheet.columns = [{   header: 'name',   key: 'name' }];  var rs = new stream.readable({ objectmode: true }); rs.push({ name: 'one' }); rs.push({ name: 'two' }); rs.push({ name: 'three' }); rs.push(null);  rs.pipe(new exceltransform({   workbook: workbook,   worksheet: worksheet })).pipe(process.stdout);