[javascript] Sum of two input value by jquery

I have code :

function compute() {
    if ($('input[name=type]:checked').val() != undefined) {
        var a = $('input[name=service_price]').val();
        var b = $('input[name=modem_price]').val();
        var total = a + b;
        $('#total_price').val(a + b);
    }
}

In my code I want sum values of two text inputs and write in a text input that has an id of "total"

My two numbers don't sum together for example :

service_price value = 2000 and modem_price=4000 in this example total input value must be 6000 but it is 20004000

use parseInt as a = parseInt($('input[name=service_price]').val())

Because at least one value is a string the + operator is being interpreted as a string concatenation operator. The simplest fix for this is to indicate that you intend for the values to be interpreted as numbers.

var total = +a + +b;

and

$('#total_price').val(+a + +b);

Or, better, just pull them out as numbers to begin with:

var a = +$('input[name=service_price]').val();
var b = +$('input[name=modem_price]').val();
var total = a+b;
$('#total_price').val(a+b);

See Mozilla's Unary + documentation.

Note that this is only a good idea if you know the value is going to be a number anyway. If this is user input you must be more careful and probably want to use parseInt and other validation as other answers suggest.

use parseInt

   var total = parseInt(a) + parseInt(b);


    $('#total_price').val(total);

if in multiple class you want to change additional operation in perticular class that show in below example

$('.like').click(function(){    
var like= $(this).text();
$(this).text(+like + +1);
});

Cast them to a Number

$('#total_price').val(Number(a)+Number(b));

But before you do that

if (!isNaN($('input[name=service_price]').val()) {...