JSFiddle - React, Tailwind, and code Playground

HTML

<form id="form-id">
  <input type="file" id="input-id" multiple="true"/>
</form>

JavaScript

function readTheFiles(file){

				var fileReader = new FileReader();
				fileReader.onloadend = function(e) {
                var fileHeader = new Uint8Array(e.target.result).subarray(0, 4);
                var header = "";
				for (var q = 0; q < fileHeader.length; q++) {
				header += fileHeader[q].toString(16);
				}
				alert(header);
				return header;				
				};
fileReader.readAsArrayBuffer(file);

} 


$("#input-id").on('change', function(event) {
            var files = event.target.files;
			var i = 0;
			for (var i = 0, file; file = files[i]; i++) {
		    
             var headString = readTheFiles(file);
		   alert(headString);
		
            }		
        });