convert callback to async/await with promise

1) Node version 8 and above now support turning callback functions into promises using the built-in util module.

const request = require('request');

const util = require('util');

const fetchData = util.promisify(request);

fetchData(url).then(data => {

   let content = JSON.parse(data.body);
   
   console.log('Joke: ', content.value);
   
}).catch(err => console.log('error: ', err))

2) Turn callback into a promise

export const mergePdfs = async (pdf1: string, pdf2: string, pdf: string) => {
  return new Promise((resolve, reject) => {
    merge([pdf1, pdf2], pdf, (error: any) => {
      if (error) {
        return reject(error)
      }
      resolve('')
    })
  })
}

3) sample for printPDF

	export const printPdf = (
	userId: string,
	listingId: string,
	listingForm: ListingForm,
	listingData: any,
	signatures: string[] //SignatureWithDate[]
	): Promise<string> => {
	return new Promise(async (resolve, reject) => {
	const localDate = formatTimestamp(new Date().toLocaleString())
	try {
	let signature: Buffer
	let signature2: Buffer
	let signatureBuffers: Buffer[] = []
	if (signatures.length > 0) {
	signature = await axios
	.get(signatures[0], {
	responseType: 'arraybuffer',
	})
	.then(response => Buffer.from(response.data, 'binary'))
	//signatureDate = localDate //signatures[0].created
	signatureBuffers.push(signature)
	if (signatures.length > 1) {
	signature2 = await axios
	.get(signatures[1], {
	responseType: 'arraybuffer',
	})
	.then(response => Buffer.from(response.data, 'binary'))
	//signature2Date = localDate //signatures[1].created
	signatureBuffers.push(signature2)
	signatureBuffers.push(signature2)
	}
	}
	const doc = new PDFDocument()
	const timestamp = Number(new Date())
	const fileName = `${userId}-${listingId}-${timestamp.toString()}.pdf`
	const { postalCode, city, stateCode, addressLine1 } = listingData
	const {
	listingFormData: { fields },
	description,
	} = listingForm
	const writeStream = fs.createWriteStream(fileName)
	doc.pipe(writeStream)
	doc.image('logo.jpg', 0, 0, { width: 220, height: 45 })
	doc.fontSize(25).text(description, 100, 100)
	doc.fontSize(25).text(`${addressLine1} ${city} ${stateCode} ${postalCode}`, 100, 300)
	fields.map((field: any) => {
	doc
	//.addPage({ margins: { top: 50, bottom: 100, left: 72, right: 72 } })
	.addPage()
	.fontSize(25)
	.text(field.title, 100, 100)
	doc.moveDown()
	const contentWidth = doc.page.width - doc.page.margins.left - doc.page.margins.right
	let cols = 0
	let nextLeft = doc.page.margins.left
	let havingFieldSetOfLastOption = false
	field.options.map((option: any) => {
	if (
	doc.y >=
	doc.page.height - doc.page.margins.bottom - signatureMargin - heightOfSignatureArea
	) {
	addSignatures(doc, signatureBuffers, localDate)
	doc.addPage()
	}
	const gridColumns = option.gridColumns['lg']
	if (gridColumns === 12 || cols >= 12 || havingFieldSetOfLastOption) {
	if ((gridColumns === 12 && cols < 12) || havingFieldSetOfLastOption) {
	doc.moveDown()
	doc.moveDown()
	}
	cols = 0
	nextLeft = doc.page.margins.left
	doc.moveDown()
	}
	doc.fillColor('#999999').fontSize(10).text(`${option.title}`, nextLeft)
	if (option.type !== 'fieldset') {
	let fieldValue
	try {
	fieldValue = listingData.data[option.key]
	} catch (error) {
	fieldValue = 'N/A'
	}
	doc.fillColor('#000000').fontSize(10).text(` ${fieldValue} `, nextLeft)
	}
	switch (gridColumns) {
	case 9:
	nextLeft += (contentWidth * 1.5) / 2
	cols += 9
	break
	case 6:
	nextLeft += contentWidth / 2
	cols += 6
	break
	case 3:
	nextLeft += contentWidth / 4
	cols += 3
	break
	default:
	break
	}
	if (cols < 12 && cols > 0) {
	doc.moveUp()
	doc.moveUp()
	}
	if (option.type === 'fieldset') {
	havingFieldSetOfLastOption = true
	let index = 0
	option.options &&
	option.options.map((o: any) => {
	const leftFs = doc.page.margins.left + ((index % 4) * contentWidth) / 4
	let fieldSetValue
	try {
	fieldSetValue = listingData.data[option.key][o.key]
	} catch (error) {
	fieldSetValue = 'N/A'
	}
	if (
	doc.y >=
	doc.page.height -
	doc.page.margins.bottom -
	heightOfSignatureArea -
	signatureMargin
	) {
	addSignatures(doc, signatureBuffers, localDate)
	doc.addPage()
	}
	if (fieldSetValue.toString() === 'true')
	doc.image('check-true.jpg', leftFs, doc.y, { width: 10, height: 10 })
	else doc.image('check-false.jpg', leftFs, doc.y, { width: 10, height: 10 })
	doc.moveUp()
	doc
	.fillColor('#0866a1')
	.fontSize(10)
	.text(`${o.title} `, leftFs + 12, doc.y + 2)
	if (o.title.length > 21 && index % 4 !== 3) index += 1
	doc.fillColor('#000000').fontSize(10).text(` `, leftFs)
	if (index !== 0 && index % 4 === 3) {
	doc.moveDown()
	} else {
	doc.moveUp()
	doc.moveUp()
	}
	index += 1
	})
	} else {
	havingFieldSetOfLastOption = false
	}
	})
	addSignatures(doc, signatureBuffers, localDate)
	})
	doc.end()
	return writeStream.on('finish', () => {
	resolve(fileName)
	})
	} catch (error) {
	reject(error)
	}
	})
	}
	const addSignatures = (doc: any, signatures: any[], signatureDate: string) => {
	const sigTop = doc.page.height - doc.page.margins.bottom - heightOfSignatureArea
	const sigDateTop = sigTop + 50
	const contentWidth = doc.page.width - doc.page.margins.left - doc.page.margins.right
	signatures.forEach((signature, idx) => {
	const left = Math.floor((contentWidth * idx) / 3) + doc.page.margins.left
	doc
	.image(signature, left, sigTop + 15, {
	width: contentWidth / 3,
	})
	.text(idx < 2 ? 'Seller' : 'Broker', left, sigTop)
	doc.fontSize(10).text(signatureDate, left, sigDateTop)
	})
	}
	let fileName
	try {
	fileName = await printPdf(uid, listingId, listingForm, listingData, signatureUrls)
	} catch (error) {
	throw new ApolloError(error, 'Print PDF error')
	}

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