Question

I have a function which does some maths on two numbers but i seem to get NaN as a return for it…. I don’t know why though….. this is my function:

function mouseConvert(mousex,mousey){

 console.log(mousex+ ' '+ mousey);

    var x = (mousex + Data.offset_x) - (settings.width/2) - settings.offset_left;
    var y = (mousey + Data.offset_y) - settings.offset_top;
    var tx = Math.round((x + y * 2) / settings.grid) - 1;
    var ty = Math.round((y * 2 - x) / settings.grid) - 1;

 console.log(tx+ ' '+ ty);

return [tx,ty];
} 

The console log output from the function shows:

Here is the value for Data and settings

Why is it not returning numbers but rather NaN ?

Answer 1

Well if the mouse positions are strings like "0", consider:

(mousex + Data.offset_x)

Becomes

"0" + -32 //"0-32"

The string "0-32" will then attempted to be converted to a number when you do subtraction with - (settings.width/2). And Number("0-32") is NaN, after which everything becomes NaN.

You should convert them to a number right at the beginning. Or rather, never convert them to strings in the first place, since the event object has them as numbers already…