JSFiddle - React, Tailwind, and code Playground

HTML

<input id="input">

<div> is Alphanumeric? 
<span id="results"></span>
</div>

JavaScript

function ctype_alnum(str) {
  var code, i, len;
	var isNumeric = false, isAlpha = false; //I assume that it is all non-alphanumeric

	
loop1:
  for (i = 0, len = str.length; i < len; i++) {
    code = str.charCodeAt(i);
		
		
		switch (true){
			case code > 47 && code < 58: // check if 0-9
				isNumeric = true;
				break;
			case (code > 64 && code < 91) || (code > 96 && code < 123): //check if A-Z or a-z
				isAlpha = true;
				break;
			default: // not 0-9, not A-Z or a-z
				return false; //stop function with false result, no more checks
				
		}

  }
	
  return isNumeric && isAlpha; //return the loop results, if both are true, the string is certainly alphanumeric
};

$("#input").on("keyup", function(){

if ($(this).val().length === 0) {$("#results").html(""); return false};
var isAlphaNumeric = ctype_alnum ($(this).val());
	$("#results").html(
		(isAlphaNumeric) ? 'Yes' : 'No'
		)
		
})