将图片转化成base64

get-image-base64.js

function getBase64Image(img, width, height) {
  var canvas = document.createElement('canvas')
  canvas.width = width ? width : img.width
  canvas.height = height ? height : img.height

  var ctx = canvas.getContext('2d')
  ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
  var dataURL = canvas.toDataURL()
  return dataURL
}