Blob实现与File DataURL canvas相互转换示例

function dataURLToBlob(fileDataURL) {
    let arr = fileDataURL.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 Blob([u8arr], {type: mime})
}

// 思路：File, Blob ——> dataURL ——> canvas

function fileAndBlobToCanvas(fileDataURL) {
    let img = new Image()
    img.src = fileDataURL
    let canvas = document.createElement('canvas')
    if(!canvas.getContext) {
      alert('浏览器不支持canvas')
      return;
    }
    let ctx = canvas.getContext('2d')
    document.getElementById('container').appendChild(canvas)
    img.onload = function() {
      ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
    }
}

function fileToDataURL(file) {
    let reader = new FileReader()
    reader.readAsDataURL(file)
    // reader 读取文件成功的回调
    reader.onload = function(e) {
      return reader.result
    }
}

function canvasToDataURL() {
    let canvas = document.createElement('canvas')
    let canvasDataURL = canvas.toDataURL('image/png', 1.0)
    return canvasDataURL
}