Question

First I test that every variable got a number value:

09-11 18:15:00.420:
       d_drop: -1.178791867393647
  drop_at_zero: 0.0731037475605623
   sightHeight: 4.5
    d_distance: 40
     zeroRange: 10

09-11 18:15:00.420:
       d_drop: true
  drop_at_zero: true
   sightHeight: true
    d_distance: true
     zeroRange: true

function isNumber (o) {
  return ! isNaN (o-0) && o != null;
}

 var d_drop; // in calculation this gets value 1.1789

 var d_path = -d_drop - sightHeight + (drop_at_zero + sightHeight) * d_distance / zeroRange;

console.log("Path: " + d_path + " cm");

and in the log:

09-11 18:15:00.430: D/CordovaLog(1533): Path: NaN cm

WHY? I have tried to figure that out couple of hours now and no success, maybe someone has an idea, I haven’t!

Thanks!
Sami

——-ANSWER IS that parse every variable when using + operand———–

var d_path = parseFloat(-d_drop) – parseFloat(sightHeight) + (parseFloat(drop_at_zero) + parseFloat(sightHeight)) * parseFloat(d_distance) / parseFloat(zeroRange);

Answer 1

The addition operator + will cast things as strings if either operand is a string. You need to parse ALL of your inputs (d_drop, sightHeight, etc) as numbers before working with them.

Here’s a demo of how the + overload works. Notice how the subtraction operator - is not overloaded and will always cast the operands to numbers:

var numberA = 1;
var numberB = 2;
var stringA = '3';
var stringB = '4';

numberA + numberB // 3 (number)
numberA - numberB // -1 (number)
stringA + stringB // "34" (string)
stringA - stringB // -1 (number)
numberA + stringB // "14" (string)
numberA - stringB // -3 (number)

http://jsfiddle.net/jbabey/abwhd/