Convert an image to base64 encoding

img_to_base64.js

/**
 * Convert an image to a base64 encoded value
 * @param {string} url - The url of the image which has correct Access-Control-Allow-Origin response header
 * @param {function} callback - callback with one parameter containing the base64 encoded value
 * @param {string} [outputFormat] - image/png or image/jpeg or image/webp(Chrome)
 */
function convertImgToBase64(url, callback, outputFormat){
  var img = new Image()
  img.crossOrigin = 'Anonymous'
  img.onload = function() {
    var canvas = document.createElement('canvas')
    var ctx = canvas.getContext('2d')
    var dataURL
    canvas.height = this.height
    canvas.width = this.width
    ctx.drawImage(this, 0, 0)
    dataURL = canvas.toDataURL(outputFormat)
    callback(dataURL)
    canvas = null
  }
  img.src = url
}