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A JavaScript function to detect the Media/Mime Type for a base64 string
/**
* Returns the data type based on the base64 string
* @param {String} base64String
* @param {String} fileName
* @returns {String}
*/
detectMimeType(base64String, fileName) {
var ext = fileName.substring(fileName.lastIndexOf(".") + 1);
if (ext === undefined || ext === null || ext === "") ext = "bin";
ext = ext.toLowerCase();
const signatures = {
JVBERi0: "application/pdf",
R0lGODdh: "image/gif",
R0lGODlh: "image/gif",
iVBORw0KGgo: "image/png",
TU0AK: "image/tiff",
"/9j/": "image/jpg",
UEs: "application/vnd.openxmlformats-officedocument.",
PK: "application/zip",
};
for (var s in signatures) {
if (base64String.indexOf(s) === 0) {
var x = signatures[s];
// if an office file format
if (ext.length > 3 && ext.substring(0, 3) === "ppt") {
x += "presentationml.presentation";
} else if (ext.length > 3 && ext.substring(0, 3) === "xls") {
x += "spreadsheetml.sheet";
} else if (ext.length > 3 && ext.substring(0, 3) === "doc") {
x += "wordprocessingml.document";
}
// return
return x;
}
}
// if we are here we can only go off the extensions
const extensions = {
xls: "application/vnd.ms-excel",
ppt: "application/vnd.ms-powerpoint",
doc: "application/msword",
xml: "text/xml",
mpeg: "audio/mpeg",
mpg: "audio/mpeg",
txt: "text/plain",
};
for (var e in extensions) {
if (ext.indexOf(e) === 0) {
var xx = extensions[e];
return xx;
}
}
// if we are here - not sure what type this is
return "unknown";
}
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