JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
入力： <input type="text" name="test" value="１２３ａｂＣ">

JavaScript

$('input[name=test]').blur(function(){
	console.log($(this).val());
  var fullSize = $(this).val();
  var halfSize = hankaku2Zenkaku(fullSize);
   console.log(halfSize);
   
})

function hankaku2Zenkaku(str) {
    return str.replace(/[Ａ-Ｚａ-ｚ０-９]/g, function(s) {
        return String.fromCharCode(s.charCodeAt(0) - 0xFEE0);
    });
}