CODEWITHSUNDEEP
javascriptphpjquery
Parthasarathi
Parthasarathi

Reputation: 99

calculate values using entered formula

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?

Upvotes: 0

Views: 149

Answers (5)

Joy Biswas
Joy Biswas

Reputation: 6527

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()">

Upvotes: 2

Paul Boutes
Paul Boutes

Reputation: 3305

You can use .eval() method which allow you to evaluates JavaScript code represented as a string. It's a really powerful method.

Then, you have to parse your formula. With this piece of code, you will be able to add expression like ((R1+R2) - (R1*3)) + 1 for example.

  function calculate(){
    var valid = true;

    var regex = /(?:[a-z$_][a-z0-9$_]*)|(?:[;={}\[\]"'!&<>^\\?:])/ig;

    var formula = document.querySelector('#formula').value;

    var R1 = parseInt(document.querySelector('#R1').value);

    var R2 = parseInt(document.querySelector('#R2').value);

    formula = formula.replace(/R1/g, R1).replace(/R2/g,R2);

    formula = formula.replace(regex, function (elm) {
      return Math.hasOwnProperty(elm)
      ? "Math."+elm
      : valid = false;
  });

  if (valid)
    alert(eval(formula));

  }

Then add onlick event on save button : 

<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="calculate()">

Here is the Working Plunker

Upvotes: -1

Sameer Anand
Sameer Anand

Reputation: 274

Infix to Prefix Conversion Algorithm: Infix to Prefix Conversion

Prefix Evaluation Algorithm: Prefix Evaluation Algorithm

Use help from these links.

Upvotes: -1

Hearner
Hearner

Reputation: 2709

<input type="button" id="save" value="save" onclick="return calculate()">

<script>
    function calculate() {
        var val1 = document.getElementById('R1').value;
        var val2 = document.getElementById('R2').value;

        var result = +val1 + +val2;
        document.getElementById('formula').value = result;
    }
</script>

Because a problem occures with "+" you have to use +val1 + +val2

Upvotes: -1

Gennady Dogaev
Gennady Dogaev

Reputation: 5991

You can use eval. This is the fastest and easiest solution, but you must be careful with it and check with regexp that formula has only R1, R2, (, ) and math operators in it.

Or (better solution) you can find a library to parse expressions, in example http://mathjs.org/docs/expressions/parsing.html

Upvotes: 0

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