check a file's header to approve or deny a file type in javascript

index.tsx
function checkFileType(file) {
    const reader = new FileReader();

    reader.onloadend = function() {
        const arr = (new Uint8Array(reader.result)).subarray(0, 4);
        let header = "";
        for (let i = 0; i < arr.length; i++) {
            header += arr[i].toString(16);
        }

        // Compare the file header with the expected header
        if (header === "89504e47") { // Expected header for PNG files
            console.log("File type approved: PNG");
        } else {
            console.log("File type denied. Unsupported file type.");
        }
    };

    reader.readAsArrayBuffer(file);
}

// Example usage
const fileInput = document.getElementById("fileInput");
fileInput.addEventListener("change", function(e) {
    const file = e.target.files[0];
    checkFileType(file);
});
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