Font string validation

if the font string is wrong, it did not set the default font back.
Look last 2 nodeDataArray parts, it set font is {font: “13px”} {font: “14px”}
see below

is there any good idea to detect font string is correct?

Call this static function, which is undocumented in the API but is documented in the go.d.ts file:
static isValidFont(font: string): boolean;