使用javascript將圖像轉換為base64

Question

 function convertImgToBase64(url){

  var canvas = document.createElement('CANVAS');
  var ctx = canvas.getContext('2d');
  var img = new Image;
  img.crossOrigin = 'Anonymous';
  img.onload = function(){
    canvas.height = img.height;
    canvas.width = img.width;
      ctx.drawImage(img,0,0);
      var dataURL = canvas.toDataURL('image/png',"");
      alert(dataURL);

      canvas = null; 
  };
  img.src = url;



}

var url_to_be_converted = "http://www.google.com/image/sample"
convertImgToBase64(url_to_be_converted);

Alert（dataURL）沒有顯示任何結果。那里沒有彈出窗口嗎？ 如何解決呢？
哪里錯了？

Answer 1

存在跨源問題...請嘗試使用此功能

function convertImgToBase64(url)
{
    var canvas = document.createElement('CANVAS');
    img = document.createElement('img'),
    img.src = url;
    img.onload = function()
    {
        canvas.height = img.height;
        canvas.width = img.width;
        var dataURL = canvas.toDataURL('image/png');
        alert(dataURL);
        canvas = null; 
    };
}

我刪除了上下文，並以另一種方式加載了圖像