前端预览图片和H5canvas压缩图片上传

/**
 * dataURL to blob, ref to https://gist.github.com/fupslot/5015897
 * @param dataURI
 * @returns {Blob}
 */
function dataURItoBlob(dataURI) {
    var byteString = atob(dataURI.split(‘,‘)[1]);
    var mimeString = dataURI.split(‘,‘)[0].split(‘:‘)[1].split(‘;‘)[0];
    var ab = new ArrayBuffer(byteString.length);
    var ia = new Uint8Array(ab);
    for (var i = 0; i < byteString.length; i++) {
        ia[i] = byteString.charCodeAt(i);
    }
    return new Blob([ab], {type: mimeString});
}

function compress(source_img_obj, quality, output_format){

        var mime_type = "image/jpeg";
        if(output_format!=undefined && output_format=="png"){
            mime_type = "image/png";
        }
        var cvs = document.createElement(‘canvas‘);
                 //naturalWidth真实图片的宽度
                 cvs.width = source_img_obj.naturalWidth;
                 cvs.height = source_img_obj.naturalHeight;
                 var ctx = cvs.getContext("2d").drawImage(source_img_obj, 0, 0);
                 var newImageData = cvs.toDataURL(mime_type, quality/100);
                 var result_image_obj = new Image();
                 result_image_obj.src = newImageData;
                 return result_image_obj;
}

var file = e.target.files[0];
var reader = new FileReader(); //读取文件对象 
reader.onload = (function(theFile) {
var img = document.getElementById("img-fileUpload_compress") //onload和onloadend
var quality =  10; //图片品质1-100
img.src = event.target.result //reader.result
window.setTimeout(function(){
var imgObj = compress(img,quality) //压缩后的图片
var src = imgObj.src; //图片的base64格式可以直接当成img的src属性值
img.src = src;
var file = dataURItoBlob(src);//转二进制
file.filename = Math.round(Math.random()*100000000000000,0)+".jpg";
// 调上传接口
},1)
});
reader.readAsDataURL(file);