如果src是base64字符串,如何获取新创建的Image()的文件大小？

Question

new Image()如果此图像src是base64数据图像,如何获得新创建的字节大小？

我有这样的coffeescript代码:

# This string is received after some original image preprocessing
base64String = "data:image/jpeg;base64......"

newImageObj = new Image()
newImageObj.src = base64String
newImageObj.onload = ->
  console.log "Resized image width is " + this.width
  console.log "New file size in bytes is " + newImageObj.fileSize

输出总是这样:

Resized image width is 500
New file size in bytes is undefined

这newImageObj.fileSize总是如此undefined.

Answer 1

这是从 base64 字符串中查找文件大小的算法：

base64String = "data:image/jpeg;base64......";

var stringLength = base64String.length - 'data:image/png;base64,'.length;

var sizeInBytes = 4 * Math.ceil((stringLength / 3))*0.5624896334383812;
var sizeInKb=sizeInBytes/1000;

Answer 2

我个人会使用类似的方法来执行上述操作，在数据格式不正确的情况下它将正常工作（例如，缺少“=”，通常无论如何都会正确解码）

new Buffer(base64String, 'base64').length