图片转base64

一、通过图片路径将图片转base64：canvas中的toDataURL

 function getBase64Image(img) {
    var canvas = document.createElement("canvas");
    canvas.width = img.width;
    canvas.height = img.height;
   var context = cavas.getContext('2d');
   context.beginPath();
   context.drawImage(img,0,0,img.width,img.height);
   var imgType = img.src.substring(img.src,lastIndexOf(".")+1).toLowerCase();  // 图片类型
   var imgBase64 = canvas.toDataURL("image/"+imgType);
   return imgBase64;
}

var img = "a.jpg";
var image = new Image();
image.src = img;
image.onload = function(){
    var base64 = getBase64Image(image);
    // console.log(base64);
}

二、只支持file、blob类型：readAsDataURL

  var img = document.getElementById('img');
function toBase64() {
  var fileReader = new FileReader();
    console.log(img.files[0]);
    fileReader.readAsDataURL(img.files[0]);
    fileReader.onload = function (ev) {
        var imgBase64Data = this.result;
        document.getElementById('base64String').value = imgBase64Data;
        document.getElementById('backImg').setAttribute('src',imgBase64Data);  // base64转 img图片
    }
}