JSFiddle - React, Tailwind, and code Playground

HTML

<input id="valorid" onblur="mostraTotal(this);" class="caixa_texto" style="width:50px;" type="text" name="extras" value="0">

JavaScript

function mostraTotal(input) {
            
     var valorUnitario = 15.00;  
     var valor =  input.value;  
     valor *= valorUnitario;  
     input.value = valor;  

}