JSFiddle - React, Tailwind, and code Playground

HTML

Main Category   
		<select  id="category" name="category" onchange="jsfunction(this)">
			<option value=""></option>
			<option value="Non-Current Asset">Non-Current Asset 11</option>
			<option value="Current Asset">Current Asset 12</option>
			<option value="Non-Current Liability">Non-Current Liability 21</option>
			<option value="Current Liability">Current Liability 22</option>
			<option value="Cost of Sales">Cost of Sales 23</option>
			<option value="Operating Expenses">Operating Expenses 31</option>
			<option value="Selling Expenses">Selling Expenses 32</option>
			<option value="Operating Income">Operating Income 41</option>
			<option value="Other Income">Other Income 42</option>
			<option value="Equity">Equity 51</option>
        </select>
        <br>
                  
        Main Code       
		<input id="main_code" type="text" name="main_code" readonly />

JavaScript

function jsfunction(element)
			{
				var text = element.options[element.selectedIndex].text;
				text = text.replace(/[^0-9]/g, '');
				document.getElementById("main_code").value=text;
            }