使用输入的公式计算值

Question

This is my html code :

<input id="R1" type="text" value="100">
<input id="R2" type="text" value="200">
<input id="formula" type="text" value="">
<input type="button" id="save" value="save">

Here the user enter formula value dynamically like R1+R2, (R1-R2)*100. I need to calculate final value using the formula.

Ex: If user enter value in formula field R1+R2; I need the result 300. How do i calculate the value dynamically ?

Answer 1

Check out this snippet, should work with any combo:

function calExpression() {
   var f = document.getElementById('formula');
   var inps = document.getElementsByTagName('input');
   var expression = f.value.toUpperCase();//' '+f.value.replace(/([-\/\+\(\)])/g,' $1 ')+' ';
   for (var i = 0; i < inps.length; i++) {
      if (inps[i].id && inps[i].type && inps[i].type.toLowerCase() === 'text') {
          expression = expression.replace(new RegExp('\\b'+inps[i].id+'\\b', 'ig'), inps[i].value);
      }
    }
    eval('f.value = '+expression+';');
}

<input id="R1" type="text" value="100">
<input id="R2" type="text" value="200">
<input id="formula" type="text" value="">
<input type="button" id="save" value="save" onclick="calcExpression()">

</div>