File Type Filter WIth JS

fileTypeFilter.js

function checkFileExtension(file, ...allowFileTypes) {
    const allowedExtensions = allowFileTypes; // List allowed extensions
    const fileExtension = file.name.split('.').pop().toLowerCase();
    return allowedExtensions.includes(fileExtension);
}

function checkContentType(file) {
    const allowedTypes = ['image/jpeg', 'image/png', 'application/zip', 'application/pdf']; // List allowed MIME types
    return allowedTypes.includes(file.type);
}

function checkMagicNumber(file) {
    return new Promise((resolve, reject) => {
        const reader = new FileReader();

        reader.onload = function (e) {
            const arrayBuffer = e.target.result;
            const uint8Array = new Uint8Array(arrayBuffer);

            // JPEG files start with 0xFFD8
            // PNG files start with 0x89504E47
            // ZIP files start with 0x504B0304
            // PDF files start with 0x25504446

            const jpegMagicNumber = uint8Array[0] === 0xFF && uint8Array[1] === 0xD8;
            const pngMagicNumber = uint8Array[0] === 0x89 && uint8Array[1] === 0x50 && uint8Array[2] === 0x4E && uint8Array[3] === 0x47;
            const zipMagicNumber = uint8Array[0] === 0x50 && uint8Array[1] === 0x4B && uint8Array[2] === 0x03 && uint8Array[3] === 0x04;
            const pdfMagicNumber = uint8Array[0] === 0x25 && uint8Array[1] === 0x50 && uint8Array[2] === 0x44 && uint8Array[3] === 0x46;

            if (jpegMagicNumber || pngMagicNumber || zipMagicNumber || pdfMagicNumber) {
                resolve(true);
            } else {
                resolve(false);
            }
        };

        reader.onerror = function () {
            reject(new Error("Error reading file"));
        };

        reader.readAsArrayBuffer(file.slice(0, 4)); // Read the first 4 bytes
    });
}

// Usage
// -------
$('#input').on('change', async function(){
	let file = ....; 
	const isValidExtension = checkFileExtension(file, 'jpg', 'png', 'jpeg');
	const isValidContentType = checkContentType(file);
	const isValidMagicNumber = await checkMagicNumber(file);

	if (isValidExtension && isValidContentType && isValidMagicNumber) {
		alert("Is Valid");
	} else {
		alert("Is NOT Valid");
	}
});