cordova - When and why number evaluates to NaN, after multiplying, in Javascript? -

from experience know, can nan when doing division or when trying make number out of string, when not contain number. there other situations, when can nan. in particular -- possible multiplication?

this piece of code, use in phonegap application:

var g = 9.80665;  acceleration.x = (acceleration.x * g).tofixed(2); acceleration.y = (acceleration.y * g).tofixed(2); acceleration.z = ((acceleration.z + 1) * g).tofixed(2); 

an acceleration base phonegap object , can hardly believe, contains string or other value, except float, result in nan.

however, in situations (on specific devices) i'm getting nan out of above.

it isn't problem me "secure" above values code this:

acceleration.x = (parsefloat(acceleration.x) || 0) + ' m/s\u00b2'; acceleration.y = (parsefloat(acceleration.y) || 0) + ' m/s\u00b2'; acceleration.z = (parsefloat(acceleration.z) || 0) + ' m/s\u00b2'; 

but, i'm curious, when , why can nan after doing multiply of values?

btw: i've read this @ mdn, many related answers here @ stack overflow, brought me no or answer question.

you'll nan when multiplying number can't converted number.

1 * '100'         // 100 because '100' converted 100 1 * ''            // 0 because '' converted 0 1 * 'ten'         // nan because 'ten' can't converted number 1 * []            // 0 because [] converted number 0 1 * [123]         // 123 because [] 123 1 * ['ten']       // nan 1 * {}            // nan 1 * true          // 1 because true 1 1 * false         // 0 1 * null          // 0 1 * undefined     // nan, undefined can't converted number 1 * function(){}  // nan 

the function 'isnan' checks if expression can converted number o not. culd check both numbers of multiplication confirm both numbers avoid errors.

for sake of completeness, know if variable nan must compare itself:

var = nan; if (a != a) console.log('a nan'); 

it happens because nan defined unequal everything, including itself.