JSFiddle - React, Tailwind, and code Playground

HTML

<input name="aendcodeM" id="aendcodeM" type="text" size="25" onKeyPress="return numchar(event)" onKeyup="autotab(this, document.form1.bendcodeM)"/>

<input name="bendcodeM" id="bendcodeM" type="text" size="25" onKeyPress="return numchar(event)" onKeyup="autotab(this, document.form1.bndwdM)"/>

JavaScript

$(document).ready(function() {
    $("input, textarea").keyup(function() {
        var val = $(this).val()
        $(this).val(val.toUpperCase());
    });
    
    $('input[type="text"]').on('keypress', function() { 
        var $this = $(this), value = $this.val(); 
        if (value.length === 1) { 
            $this.val( value.charAt(0).toUpperCase() );
        }  
    });
})