json-csv/src/exporter.js

Easily convert JSON array to CSV in Node.JS via buffered or streaming.

const { Transform, Readable } = require('stream')
const StringWriter = require('./string-writer')

class CsvExporter {
	constructor(options = {}) {
		this.options = { ...options } // shallow
		if (options.fieldSeparator == null) this.options.fieldSeparator = ','
		if (options.ignoreHeader == null) this.options.ignoreHeader = false
		if (options.buffered == null) this.options.buffered = true
		if (options.fields == null) this.options.fields = []
		if (options.encoding == null) this.options.encoding = 'utf8'
	}

	// alias
	buffered(data) {
		return new Promise((resolve, reject) => {
			let writer = new StringWriter({ defaultEncoding: 'utf8' })
			let readable = Readable.from(data.map(d => d === null ? {} : d))
				.pipe(this.stream())
			readable.on('error', reject)
			readable.pipe(writer)
				.on('finish', () => {
					resolve(writer.data)
				})
		})
	}

	stream() {
		let writtenHeader = false
		let { ignoreHeader, fields, encoding } = this.options
		// eslint-disable-next-line @typescript-eslint/no-this-alias
		let self = this

		let transformer = new Transform({
			writableObjectMode: true,
			transform(chunk, _encoding, callback) {
				// debug(`incoming chunk: ${require('util').inspect(chunk)}`)
				// debug(encoding)
				if (!writtenHeader && !ignoreHeader) {
					writtenHeader = true
					let header = self.getHeaderRow(fields)
					// debug(`writing header ${header}`)
					this.push(header)
				}
				let row = self.getBodyRow(chunk, fields)
				// debug(`writing row ${require("util").inspect(row)}`)
				this.push(row)
				callback()
			}
		})
		transformer.setEncoding(encoding)
		return transformer
	}

	prepValue(arg, forceQuoted) {
		var quoted = forceQuoted || arg.indexOf('"') >= 0 || arg.indexOf(this.options.fieldSeparator) >= 0 || arg.indexOf('\n') >= 0
		var result = arg.replace(/"/g, '""')
		if (quoted) { result = '"' + result + '"' }
		return result
	}

	getHeaderRow(fields) {
		let fieldKeys = Object.keys(fields)
		var header = fieldKeys.reduce((line, fieldKey) => {
			let field = fields[fieldKey]
			var label = field.label || field.name
			if (line === 'START') {
				line = ''
			} else {
				line += this.options.fieldSeparator
			}
			line += this.prepValue(label)
			return line
		}, 'START')
		header += '\r\n'
		return header
	}

	getBodyRow(data, fields) {
		let reducer = (line, field) => {
			if (line === 'START') {
				line = ''
			} else {
				line += this.options.fieldSeparator
			}
			var val = this.getValue(data, field.name)
			// vinicioslc support to OR || operator  allowing multiples names to the same column
			// the code will use the last non null and non empty value
			if (field.name.includes('||')) {
				// by default column is empty
				val = ''
				let fields = field.name.split('||')
				// for each alternative
				fields.forEach((field) => {
					// get value and associate
					let fieldVal = this.getValue(data, field)
					// remove whitespaces and check if non null before assign
					if (val != null && fieldVal.trim().length > 0 && fieldVal.trim() !== '') {
						val = fieldVal
					}
					// do this for every field
				})
			}

			if (typeof field.transform === 'function') {
				val = field.transform(val)
			} else if (typeof field.filter === 'function') {
				val = field.filter(val)
			}
			if (typeof val !== 'undefined' && val !== null) {
				var quoted = typeof field.quoted !== 'undefined' && field.quoted
				line += this.prepValue(val.toString(), quoted)
			}
			return line
		}

		var row = fields.reduce(reducer, 'START')
		row += '\r\n'
		return row
	}

	getValue(data, arg) {
		var args = arg.split('.')
		if (args.length > 0) return this.getValueIx(data, args, 0)
		return ''
	}

	getValueIx(data, args, ix) {
		if (!data) { return '' }

		// for filtered fields using the whole row as a source.
		// `this` is a keyword here; hoping not to conflict with existing fields.
		if (args[0] === 'this') { return data }

		var val = data[args[ix]]
		if (typeof val === 'undefined') { return '' }

		// walk the dot-notation recursively to get the remaining values.
		if ((args.length - 1) > ix) { return this.getValueIx(val, args, ix + 1) }

		return val
	}
}

module.exports = CsvExporter