js中 文件、圖片二進制和base64的互轉

/**
 * 網絡圖像文件轉Base64
 */
function getBase64Image(img) {
    var canvas = document.createElement("canvas");
    canvas.width = img.width;
    canvas.height = img.height;
    var ctx = canvas.getContext("2d");
    ctx.drawImage(img, 0, 0, img.width, img.height);
    var ext = img.src.substring(img.src.lastIndexOf(".") + 1).toLowerCase();
    var dataURL = canvas.toDataURL("image/" + ext);
    return dataURL;
}
 
 
/**
*Base64字符串轉二進制
*/
function dataURLtoBlob(dataurl) {
    var arr = dataurl.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
    });
}
 
 
var img = "圖像文件URL地址";
var image = new Image();
image.src = img;
image.onload = function() {
    //這樣就獲取到了文件的Base64字符串
    var base64 = getBase64Image(image);
    //Base64字符串轉二進制
    var file = dataURLtoBlob(base64);
}