Question

How can i prevent to javascript interpret my numeric vars from string vars?

var a = 100;
var b = -10
var c = a + b // 10-10 (string)

lets say i allways want

var c = a + b = 100+(-10) = 90 (number)

Answer 1

In your example c will always be 90, however;

var a = 100;
var b = "-10";
var c = a + b // "100-10" (string)

to prevent this convert the string to an integer;

var c = a + parseInt(b, 10); 

or with a unary+

var c = a + +b;