I want to create a function for use in a pipe() call in Gulp that'll enable conversion of xlsx files to json.
I had this working with NPM package 'excel-as-json' for gulp 3, however Gulp 4 has forced me to actually understand what it is doing ;-)
Six hours in, and my incapacity of getting this to work due to a lack of js/async/streaming knowledge is punching my curiosity.
Code is as follows:
paths = {excel_sourcefiles: "./sourcefiles/*.xls*", excel_targetdir_local_csvjson: "./targetfiles_local/*.*"}
var replaceExt = require('replace-ext');
var PluginError = require('plugin-error')
var gulpFunction = require('gulp-function').gulpFunction // default ES6 export
var through = require("through2")
var convertExcel = require('excel-as-json').processFile;
var changed = require('gulp-changed');
var assign = Object.assign || require('object.assign');
var notify = require('gulp-notify');
var gulpIgnore = require('gulp-ignore');
var rename = require('gulp-rename');
gulp.task('excel-to-jsoncsv', function() {
return gulp.src(paths.excel_sourcefiles)
// .pipe(debug())
.pipe(gulpIgnore.exclude("*\~*")) // Ignore temporary files by Excel while xlsx is open
.pipe(gulpIgnore.exclude("*\$*")) // Ignore temporary files by Excel while xlsx is open
.pipe(plumber({errorHandler: notify.onError('gulp-excel-to-jsoncsv error: <%= error.message %>')}))
.pipe(changed(paths.excel_targetdir_local_glob, { extension: '.csv' }))
.pipe(GulpConvertExcelToJson()) // This is where the magic should happen
.pipe(rename({ extname: '.csv' })) // Saving as .csv for SharePoint (does not allow .json files to be saved)
.pipe(gulp.dest(paths.excel_targetdir_local))
});
function GulpConvertExcelToJson() {
return through.obj(function(chunk, enc, callback) {
var self = this
if (chunk.isNull() || chunk.isDirectory()) {
callback() // Do not process directories
// return
}
if (chunk.isStream()) {
callback() // Do not process streams
// return
}
if (chunk.isBuffer()) {
convertExcel(chunk.path, null, null, // Converts file found at `chunk.path` and returns (err, `data`) its callback.
function(err, data) {
if (err) {
callback(new PluginError("Excel-as-json", err))
}
chunk.contents = new Buffer(JSON.stringify(data))
self.push(chunk)
callback()
// return
})
} else {
callback()
}
})
}
I (now) know there are other excel > json gulp modules that could allow me to solve this problem without writing my own module, yet I'd like to understand what I should do different here.
The error returned is 'Did you forget to signal Async completion?', which I tried to not do. However, probably my attempt to fix the error 'this.push is not a function' with a var self = this is not what I was supposed to do.
Looking at examples like gulp-zip introduced me to unfamiliar notations, making me unable to autodidact my way out of this.
In summary:
- how would I go about calling an async function during a through.obj function call, where the chunk's contents is updated with the (not under my control) async function that only provides me with a callback (err, data)?
