jQuery perform maths operation

Question

HTML User Input:

=110*200

jQuery:

   $(document).on("change", ".calculator", function(){
        var value = $(this).val();
        if(value.charAt(0) == '='){
            var newval = value.slice(1);
            console.log(parseInt(newval));
        }
    })

Output:

110

Anyone can please tell me How can I perform maths operation by using this programme? Where am I going wrong And Why it not working?

Answer 1

This is happening because you never evaluate the expression itself. You cast string expression to integer, and it takes identifiable integer part from the expression, breaking it at * character.

Evaluate your expression with eval, and it will get calculated. Alternatively, you can also use Function construct as described in answer here to evaluate this expression.

$(document).on("change", ".calculator", function(){
        var value = $(this).val();
        console.log(value.charAt(0));
        if(value.charAt(0) == '='){
            var newval = value.slice(1);
            console.log(parseInt(eval(newval)));
            console.log(new Function('return ' + newval)());
        }
    })
    
  

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input class="calculator" type="text">