blog/gatsby/createExifFields.js

const fastExif = require('fast-exif')
const Fraction = require('fraction.js')
const dms2dec = require('dms2dec')

exports.createExifFields = (node, createNodeField) => {
  fastExif
    .read(node.absolutePath, true)
    .then(exifData => {
      if (!exifData) return
      constructExifFields(exifData, createNodeField, node)
    })
    .catch(() => null) // just silently fail when exif can't be extracted
}

const constructExifFields = (exifData, createNodeField, node) => {
  const { Model } = exifData.image
  const {
    ISO,
    FNumber,
    ExposureTime,
    FocalLength,
    ExposureBiasValue
  } = exifData.exif
  const {
    GPSLatitudeRef,
    GPSLatitude,
    GPSLongitudeRef,
    GPSLongitude
  } = exifData.gps

  const { n, d } = new Fraction(ExposureTime)
  const exposureShortened = parseFloat(ExposureBiasValue.toFixed(2))

  const model = `${Model}`
  const iso = `ISO ${ISO}`
  const fstop = `ƒ ${FNumber}`
  const shutterspeed = `${n}/${d}s`
  const focalLength = `${FocalLength}mm`

  const GPSdec = dms2dec(
    GPSLatitude,
    GPSLatitudeRef,
    GPSLongitude,
    GPSLongitudeRef
  )

  const latitude = GPSdec[0]
  const longitude = GPSdec[1]

  let exposure

  if (ExposureBiasValue === 0) {
    exposure = `+/- ${exposureShortened} ev`
  } else if (ExposureBiasValue > 0) {
    exposure = `+ ${exposureShortened} ev`
  } else {
    exposure = `${exposureShortened} ev`
  }

  // add exif fields to type File
  createNodeField({
    node,
    name: 'exif',
    value: {
      iso,
      model,
      fstop,
      shutterspeed,
      focalLength,
      exposure,
      gps: {
        latitude,
        longitude
      }
    }
  })
}