关于canvas:将canvas作为图片下载

思路是将 canvas 转化为 base64 链接，通过模仿 a 标签的 download 属性进行下载

// https://stackoverflow.com/questions/18480474/how-to-save-an-image-from-canvas
function download(canvas, filename) {var lnk = document.createElement('a'), e
  lnk.download = filename
  lnk.href = canvas.toDataURL('image/png;base64')

  if(document.createEvent) {e = document.createEvent('MouseEvents')
    e.initMouseEvent('click', true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null)
    lnk.dispatchEvent(e)
  } else if(lnk.fireEvent) {lnk.fireEvent('onclick')
  }
}

放一个 html 的 Demo

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Download Cavans</title>
  <style>
    *{
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }
    html,body{
      height: 100%;
      width: 100%;
    }
    .wrapper{
      width: 100%;
      height: 100%;
      padding: 100px;
      display: flex;
      flex-direction: column;
      justify-content: space-around;
      align-items: center;
    }
    .button{
      width: 100px;
      height: 40px;
      display: flex;
      justify-content: center;
      align-items: center;
      border: 1px solid #ddd;
      box-shadow: 2px 2px 14px #333;
      cursor: pointer;
      user-select: none;
      transition: all .3s;
    }
    .button:hover{transform: skew(-15deg);
    }
  </style>
</head>
<body>
  <div class="wrapper">
    <div class="button">Download</div>
  </div>
  <script>
    var wrapper = document.querySelector('.wrapper')
    var canvas = document.createElement('canvas')
    canvas.width = 500
    canvas.height = 500
    var ctx = canvas.getContext('2d')
    ctx.fillStyle = 'rgba(0, 0, 225, .6)'
    ctx.fillRect(0, 0, 500, 500)
    ctx.fillStyle = 'rgba(225, 0, 0, .6)'
    ctx.font = '600 40px Arial'
    ctx.fillText('Canvas', 100, 100)
    wrapper.appendChild(canvas)

    function download(canvas, filename) {var lnk = document.createElement('a'), e
      lnk.download = filename

      lnk.href = canvas.toDataURL('image/png;base64')

      if(document.createEvent) {e = document.createEvent('MouseEvents')
        e.initMouseEvent('click', true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null)
        lnk.dispatchEvent(e)
      } else if(lnk.fireEvent) {lnk.fireEvent('onclick')
      }
    }

    document.querySelector('.button').onclick = () => {download(canvas, 'image.png')
    }
  </script>
</body>
</html>

将 canvas 作为图片下载