base64-image-mime/index.js

Get mimetype from base64-encoded images

const atob = require('atob')
const Buffer = require('buffer/').Buffer
const mimeTypes = {
  png: 'image/png',
  gif: 'image/gif',
  jpg: 'image/jpeg',
  svg: 'image/svg+xml',
  webp: 'image/webp',
  jpeg: 'image/jpeg',
  pjpeg: 'image/jpeg',
  pjp: 'image/jpeg',
  jfif: 'image/jpeg'
}

function getImageMime(base64Encoded) {
  if (base64Encoded.startsWith('data:')) {
    const found = base64Encoded.match(/data:\S*;base64/g)
    return found && found[0].slice('data:'.length, ';base64'.length * -1)
  } else {
    const prefix = atob(base64Encoded.slice(0, 60))
    const found = prefix.match(/(webp)|(png)|(gif)|(svg)|(jpg)|(jpeg)|(pjpeg)|(pjp)|(jfif)/gi)
    if (!found) {
      const hex = Buffer.from(base64Encoded, 'base64').toString('hex')
      if (hex.startsWith('ffd8ff')) return mimeTypes.jpeg
      return null
    } else {
      const type = found[0].toLocaleLowerCase()
      return mimeTypes[type]
    }
  }
}

module.exports = {
  getImageMime: getImageMime
}