JSFiddle - React, Tailwind, and code Playground

HTML

<input class="onealphaonly">

JavaScript

$('.onealphaonly').bind('keyup keypress blur',function(e){ 
    var node = $(this);
    var val = node.val();
    if (val.length >= 1) {
    	e.preventDefault();
      return false;
    }
    node.val( val.substr(0,1) );
});