Check the header to see the file type

MimeTypeVerification.js

//https://stackoverflow.com/questions/18299806/how-to-check-file-mime-type-with-javascript-before-upload/29672957#29672957
	// Return the first few bytes of the file as a hex string
	function getBLOBFileHeader(url, blob, callback) {
		var fileReader = new FileReader();
		fileReader.onloadend = function (e) {
			var arr = (new Uint8Array(e.target.result)).subarray(0, 4);
			var header = "";
			for (var i = 0; i < arr.length; i++) {
				header += pad(arr[i].toString(16), 2);
			}
			callback(url, header);
		};
		fileReader.readAsArrayBuffer(blob);
	}

	function pad(num, size) {
		var s = "0000" + num;
		return s.substr(s.length - size);
	}

	function headerCallback(url, headerString) {
		printHeaderInfo(url, headerString);
	}

	function remoteCallback(url, blob) {
		getBLOBFileHeader(url, blob, headerCallback);
	}

	// Add more from http://en.wikipedia.org/wiki/List_of_file_signatures
	function mimeType(headerString) {
		switch (headerString.toLowerCase()) {
			case "89504e47":
				type = "image/png";
				break;
			case "47494638":
				type = "image/gif";
				break;
			case "ffd8ffe0":
				type = "jpg"
				break;
			case "ffd8ffe1":
				type = "jpg"
				break;
			case "ffd8ffdb":
				type = "jpg"
				break;
			case "ffd8ffe2":
				type = "image/jpeg";
				break;
			case "25504446":
				type = "pdf";
				break;
			case "7b5c7274": //6631
				type = "rtf";
				break;
			case "504b0304":
				type = "zip archive (Office)";
				break;
			case "504b0506":
				type = "zip archive empty";
				break;
			case "504b0708":
				type = "zip archive spanned";
				break;
			case "49492a00":
				type = "TIF (little endian format)";
				break;
			case "4d4d002a":
				type = "TIF (big endian format)";
				break;
			case "d0cf11e0": //a1b11ae1
				type = "Old Office Format";
				break;
			default:
				type = "Unsupported";
				break;
		}
		return type;
	}

	function printHeaderInfo(url, headerString) {
		console.log("File Type: " + mimeType(headerString));
	}

	// Check for FileReader support
	if (window.FileReader && window.Blob) {
		/* Handle local files */
		$("input").on('change', function (event) {
			var file = event.target.files[0];
			if (file.size >= 100 * 1024 * 1024) {
				alert("File size must be at most 100MB");
				return;
			}
			remoteCallback(escape(file.name), file);
		});

	} else {
		// File and Blob are not supported
		alert("Your browser is not supported");
	}