从 Base64 字符串创建 TypedArray

var data = 
   'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACN' +
   'byblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHx' +
   'gljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';

var characters = atob(data);

var array = new Uint8Array(characters.length);

for (var i = 0; i < characters.length; i++) {
  array[i] = characters.charCodeAt(i);
}