Testing to see if I can build an Opentype Panel

FontSpike.js

framework("CoreText");

const document = require("sketch").getSelectedDocument();

const textLayer = document.selectedLayers.layers[0];

//	WORKS (System font has native support for small caps):

const font = NSFont.systemFontOfSize_weight(28, NSFontWeightBold);

//	DOESN'T WORK: (Depending on if the existing font has small caps support:

// const font = textLayer.font;

//	Two notes:
//	1. Had to look it up, [] in ES6 brackets can be used to use variables as object literal keys -
//	before you were actually using "NSFontFeatureSettingsAttribute" instead of what that variable is set to, which is "CT"-something
//	2. kLowerCaseType & kLowerCaseSmallCapsSelector are defined in the CoreText framework

const descriptor = font.fontDescriptor().fontDescriptorByAddingAttributes({
    [NSFontFeatureSettingsAttribute]: [{
		[NSFontFeatureTypeIdentifierKey]: kLowerCaseType,
		[NSFontFeatureSelectorIdentifierKey]: kLowerCaseSmallCapsSelector
	}]
});

const newFont = NSFont.fontWithDescriptor_size(descriptor, 20);

//	- Using _object here worked, but it's the private version of the public sketchObject property.
//	Using _object or sketchObject gave you the MSTextLayer (internal Sketch Objective-C class)
//	that the Sketch JS library Text object (textLayer) wraps.
//	- The Text object has the font property so we _should_ be able to use that, but for whatever reason it's not working, so...

textLayer.sketchObject.setFont(newFont);

document.sketchObject.inspectorController().reload();