CODE EXAMPLE FOR JAVASCRIPT

calculate string value in javascript

<div>
  <label for="input">Equation: </label>
  <input type="text" id="input" value="12/5*9+9.4*2-1" />
  <input type="button" 
         value="calculate" 
         onclick="getElementById('result').value = calculate(getElementById('input').value)" />
</div>

<div>
  <label for="result">Result: </label>
  <input type="text" id="result" />
</div>