File、URL、Base64、Blob、ArrayBuffer格式转换，图片压缩_dataurltofile

目录

url 转 base64

File 转 Base64

base64转File对象 

dataURL转 File 对象

base64转ArrayBuffer对象

base64转blob

blob转File

图片压缩

---

url 转 base64

/**
* url转base64
* @param {String} url - url地址
* 可能会存在跨域问题，可以尝试转之前在url链接后面加?v=1这种方式，跟服务器更新代码文件清缓存一个原理
*/
urlToBase64(url) {
      return new Promise ((resolve,reject) => {
        let image = new Image();
        image.setAttribute("crossOrigin",'Anonymous');
        image.src = url;
        image.onload = function() {
            let canvas = document.createElement('canvas');
            canvas.width = this.naturalWidth || "300px";
            canvas.height = this.naturalHeight || "300px";
            // 将图片插入画布并开始绘制
            canvas.getContext('2d').drawImage(image, 0, 0);
            // result
            let result = canvas.toDataURL('image/png')
            resolve(result);
        };
        // 图片加载失败的错误处理
        image.onerror = () => {
            reject(new Error('转换失败'));
        };
      });
    },

File 转 Base64

fileToBase64(e) {
      let file = e.target.files[0];
      let reader = new FileReader();
      //读取为base64
      reader.readAsDataURL(file)
      // 读取操作完成触发
      reader.onload = (e) => {
        let data;
        if (typeof e.target.result === 'object') {
          // 把Array Buffer转化为blob 如果是base64不需要 
          data = window.URL.createObjectURL(new Blob([e.target.result])) // 转化为url
        } else {
          data = e.target.result;
        }
        // 因为调用了readAsDataURL方法规定将文件读取为base64,所以data为当前选择文件的base64形式
        return data;
      }
    },
 
fileToBase64Async(file) {
        return new Promise((resolve, reject) => {
          let reader = new FileReader();
          reader.readAsDataURL(file);
          reader.onload = (e) => {
            resolve(e.target.result);
          };
        });
      },

base64转File对象 

parseBase64(base64) {
        let arr = base64.split(","),
            mime = arr[0].match(/:(.*?);/)[1];
        return {
          mime,
          data: arr[1],
        };
      },
base64ToUint8Array(base64) {
        let parsedBase64 = this.parseBase64(base64);
        let bstr = atob(parsedBase64.data);
        let n = bstr.length;
        let u8arr = new Uint8Array(n);
        while (n--) {
          u8arr[n] = bstr.charCodeAt(n);
        }
        return u8arr;
      },
base64ToFile(base64, fileName) {
        let file = null;
        // 浏览器兼容
        if (window.File != undefined) {
          let parsedBase64 = this.parseBase64(base64);
          let u8arr = this.base64ToUint8Array(base64);
          file = new File([u8arr], fileName, {
            type: parsedBase64.mime,
          });
        } else {
          file = this.blobToFile(base64ToBlob(base64));
        }
        return file;
      }

dataURL转 File 对象

dataURLtoFile(dataUrl, fileName){
    var arr = dataUrl.split(','), mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
    while(n--){
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new File([u8arr], fileName, {type:mime});
}

base64转ArrayBuffer对象

function base64ToArrayBuffer(base64) {
  base64 = base64.replace(/^data\:([^\;]+)\;base64,/gmi, '')
  var binary = atob(base64)
  var len = binary.length
  var buffer = new ArrayBuffer(len)
  var view = new Uint8Array(buffer)
  for (var i = 0; i < len; i++) {
    view[i] = binary.charCodeAt(i)
  }
  return buffer
}

base64转blob

 
base64ToBlob(base64Val) {
  const arr = base64Val.split(',');
  // 注意base64的最后面中括号和引号是不转译的   
  const _arr = arr[1].substring(0,arr[1].length-2);
  const mime = arr[0].match(/:(.*?);/)[1],
    bstr =atob(_arr),
    n = bstr.length,
    u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new Blob([u8arr], {
    type: mime
  });
}

blob转File

blobToFile(blobData) {
        let date = new Date();
        blobData.lastModifiedDate = date;
        blobData.lastModified = date.getTime();
        blobData.name = blobData.type.replace("/", ".");
        return blobData;
      },

图片压缩

//压缩图片
export function compressImg(file,target = {}){
    var files,name = file.name;
    var fileSize = parseFloat(parseInt(file['size'])/1024/1024).toFixed(2);
    var read = new FileReader();
    read.readAsDataURL(file);
    return new Promise(function(resolve, reject){
        read.onload = function (e) {
            var img = new Image();
            img.src = e.target.result;
            img.onload = function(){
                //默认按比例压缩
                var w = target.width || "200px",
                    h = target.height || "200px";
                //生成canvas
                var canvas = document.createElement('canvas');
                var ctx = canvas.getContext('2d');
                var base64;
                // 创建属性节点
                canvas.setAttribute("width", w);
                canvas.setAttribute("height", h);
                ctx.drawImage(this, 0, 0, w, h);
                if(fileSize<1){
                    //如果图片小于一兆 那么不执行压缩操作
                    base64 = canvas.toDataURL(file['type'], 1);
                }else if(fileSize>1&&fileSize<2){
                    //如果图片大于1M并且小于2M 那么压缩0.5
                    base64 = canvas.toDataURL(file['type'], 0.5);
                }else{
                    //如果图片超过2m 那么压缩0.2
                    base64 = canvas.toDataURL(file['type'], 0.2);
                }
                // 回调函数返回file的值（将base64编码转成file）
                files = dataURLtoFile(base64,name); //如果后台接收类型为base64的话这一步可以省略
                resolve(files)
            };
        };
    })
};