前端url創建，以及base64與url的轉化

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 });
}
function getObjectURL(file) {
    var url = null;
    if (window.createObjectURL !== undefined) { // basic
        url = window.createObjectURL(file);
    } else if (window.URL !== undefined) { // mozilla(firefox)
        url = window.URL.createObjectURL(file);
    } else if (window.webkitURL !== undefined) { // webkit or chrome
        url = window.webkitURL.createObjectURL(file);
    }
    return url;
}