使用 JavaScript 下載圖像

Question

我正在使用 JavaScript 代碼來上傳、預覽和下載圖像。 目前我已經完成了上傳和預覽代碼。 之后，如何下載呢？

    <section class="upload" id="upload">
            <h3>UPLOAD</h3>
          
          <div class="container">
            <div class="row">
              
              <canvas id="c" class="p-3" >Here's the canvas.</canvas>
              <br>
              <input type="file" id="infile" accept = "image/*" onchange="handleFiles(this.files)">
              <p><img id="output" /></p>
              <button onclick="blurimg()" class="btnbl">Blur Image</button>
              <br>
             </div>
            </div>
      
    </section>

     //Canvas creating with image
        document.getElementById('infile').onchange = function(e) {
          var img = new Image();
          img.onload = draw;
          img.onerror = failed;
          img.src = URL.createObjectURL(this.files[0]);
        };
        function draw() {
          var canvas = document.getElementById('c');
          canvas.width = this.width;
          canvas.height = this.height;
          var ctx = canvas.getContext('2d');
          ctx.drawImage(this, 0,0);
        }
        function failed() {
          console.error("The provided file couldn't be loaded as an Image media");
        }

Answer 1

你可以在HTML檢查這個例子： https://www.w3schools.com/tags/att_a_download.asp

Answer 2

未經測試，但它會是這樣的：

async function downloadCanvas () {
  const type = 'image/jpeg'
  const quality = 1
  const blob = await new Promise(rs => canvas.toBlob(rs, type, quality)
  const link = document.createElement('a')
  a.href = URL.createObjectURL(blob)
  a.download = 'cat.jpg'
  a.click()
}

如果您想要並支持更新的瀏覽器，那么您可以使用bitmap = await createImageBitmap(file)而不是繪制<img>