TypeScript error when using Chart.defaults.font.size = 8; in v 3.6.0

[doberkofler]

Current Behavior

After upgrading from 3.5.1 to 3.6.0 the following statement reports a TypeScript error:

Chart.defaults.font.size = 8;

index.ts:181:22 - error TS2339: Property 'size' does not exist on type 'Scriptable<Partial<FontSpec>, ScriptableContext<keyof ChartTypeRegistry>>'.
  Property 'size' does not exist on type '(ctx: ScriptableContext<keyof ChartTypeRegistry>, options: AnyObject) => Partial<FontSpec> | undefined'.

181  Chart.defaults.font.size = 8;

Environment

• Chart.js version: 3.6.0

[etimberg]

I believe that this is related to #9680 which added partial<> around the FontSpec object. This typing is technically correct since these fields are not required.

You could use Chart.defaults.set('font', { size: 8 }) but you'll lose the type checking on the properties. @kurkle I'm not sure what the best option is here. My initial thought was to change the Defaults type to indicate what we ship as defaults but a user can change that at any time.

[JacoBriers]

This bit me recently when I tried to appease the type checker by doing:

Chart.defaults.font = {
  family: 'Roboto, "Helvetica Neue", Arial, sans-serif',
};

This broke things in weird and wonderful ways and took me a day to debug 😢 . Thanks for this fix!