javascript - 转换图像应该有一些小的 url 而不是基本代码

Question

现在我正在将图像上传到 Canvas 中，上传图像后， Canvas 通过 toDataURl 转换为图像。如果我通过 toDataURL 将 Canvas 转换为图像，那么我将获得基本代码(基本代码会很大)。我想要一些小的 url 而不是 BaseCode。

var canvas = new fabric.Canvas('canvas');
document.getElementById('file').addEventListener("change", function (e) {
  var file = e.target.files[0];
  var reader = new FileReader();
  reader.onload = function (f) {  
    var data = f.target.result;  
    var img = document.createElement('img');
                    img.src = data;
                    img.onload = function () {
                        if (img.width < 300 || img.height < 300)
                        {
                            alert("upload image should be greater");
                            canvas.getActiveObject().remove();
                        }
                    };
    
    fabric.Image.fromURL(data, function (img) {
      var oImg = img.set({left: 50, top: 100,width:100, height:100, angle: 00}).scale(0.9);
      canvas.add(oImg).renderAll();
      var a = canvas.setActiveObject(oImg);
      var dataURL = canvas.toDataURL({format: 'png', quality: 0.8});
      console.log("aaaaaaaaaaa" + dataURL);

      //                        console.log("Canvas Image " + dataURL);
      //                        document.getElementById('txt').href = dataURL;

    });
  };
  reader.readAsDataURL(file);
});
document.querySelector('#txt').onclick = function (e) {
  e.preventDefault();
  canvas.deactivateAll().renderAll();
  document.querySelector('#preview').src = canvas.toDataURL();
  var b= canvas.toDataURL();
  console.log(b);
}

canvas{
  border: 1px solid black;
}

<script src="https://rawgit.com/kangax/fabric.js/master/dist/fabric.min.js"></script>
<input type="file" id="file">
<canvas id="canvas" width="400" height="400"></canvas>
<a href='' id='txt' target="_blank">Click Me!!</a>
<br />
<img id="preview" />

JSFiddle:https://jsfiddle.net/varunPes/8gt6d7op/23/

Answer 1

The devil is in the details - nowhere in the question do you even suggest you want to send the image somewhere - the code below is limited to the client - you can only use the short form url on the client, and as mentioned in a comment, only for a session (restart browser, url is useless), or until revokeObjectURL is called

你可以 - 如果浏览器支持，使用 Blob，它的 URL 很短

// converts a dataURI to a Blob
function dataUriToBlob(dataURI) {
    var byteString = atob(dataURI.split(',')[1]);
    var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0];
    var arrayBuffer = new ArrayBuffer(byteString.length);
    var _ia = new Uint8Array(arrayBuffer);
    for (var i = 0; i < byteString.length; i++) {
        _ia[i] = byteString.charCodeAt(i);
    }
    var dataView = new DataView(arrayBuffer);
    var blob = new Blob([dataView], { type: mimeString });
    return blob;
}
// cross browser cruft
var get_URL = function () {
    return window.URL || window.webkitURL || window;
};
// ... your code, which eventually does this
var b = canvas.toDataURL();
// get an URL from the Blob
var blob = dataUriToBlob(b);
var url = get_URL().createObjectURL(blob);
console.log(url);
//
// ... when finished with the object URL
URL.revokeObjectURL(url);