javascript string to number = NaN

Question

I am studying Javascript. Can someone please tell me what I'm not doing right?

 total = pdf_tp_summa+2490+(Number(elem_summa_sms.value))+(Number(elem_summa_push.value)); 

NaN total outputs in Console.

 typeof(pdf_tp_summa) = number typeof(elem_summa_sms.value) = string typeof(elem_summa_push.value) = string 

Answer 1

The result is NaN. It is how javascript works.

//elem_summa_push.value is string, so 
Number(elem_summa_push.value)//eg. Number('asdf')

Would result in NaN.

And when you add any number to the NaN it would result NaN.

If the elem_summa_push.value is type of string but still contains number then it wouldn't result in NaN. For eg. Number('234')