图片路径转为base64

function dealImage(path, callback){  
    var img = new Image();  
    img.src = path;  
    img.onload = function(){  
        //默认按比例压缩  
        var w = this.width,  
            h = this.height; 
        var quality = 0.95; // 默认图片质量为0.7  
          
        //生成canvas  
        var canvas = document.createElement('canvas');  
        var ctx = canvas.getContext('2d');  
          
        // 创建属性节点  
        canvas.setAttribute("width", w);  
        canvas.setAttribute("height", h);
                
        ctx.drawImage(this, 0, 0, w, h);  
        // quality值越小，所绘制出的图像越模糊  
        var base64 = canvas.toDataURL('image/jpeg', quality);  
        // 回调函数返回base64的值  
        callback(base64);  
    };  
};