How to make a stroke layer style using a script?

This one creates a gradient stroke style using a gradient preset of "Foreground to Background". The gradient-related values are at defaults.

// Uses a gradient preset named "Foreground to Background"

// Get the foreground RGB values
var fR = foregroundColor.rgb.red;
var fG = foregroundColor.rgb.green;
var fB = foregroundColor.rgb.blue;

// Get the background RGB values
var bR = backgroundColor.rgb.red;
var bG = backgroundColor.rgb.green;
var bB = backgroundColor.rgb.blue;

setGradStrokeStyle(100, true, true, true, 100, 3, 128, 128, 128, "Foreground to Background", 4096, fR, fG, fB, 0, 50, bR, bG, bB, 4096, 50, 100, 0, 50, 100, 4096, 50, 90, false, false, 100, true, 0, 0, false);

function setGradStrokeStyle(scale, enabled, present, showInDialog, opacity, size, red, grain, blue, name2, interfaceIconFrameDimmed, red2, grain2, blue2, location, midpoint, red3, grain3, blue3, location2, midpoint2, opacity2, location3, midpoint3, opacity3, location4, midpoint4, angle, reverse, dither, scale2, align, horizontal, vertical, overprint) {
	var s2t = function (s) {
		return app.stringIDToTypeID(s);
	};

	var descriptor = new ActionDescriptor();
	var descriptor2 = new ActionDescriptor();
	var descriptor3 = new ActionDescriptor();
	var descriptor4 = new ActionDescriptor();
	var descriptor5 = new ActionDescriptor();
	var descriptor6 = new ActionDescriptor();
	var descriptor7 = new ActionDescriptor();
	var descriptor8 = new ActionDescriptor();
	var descriptor9 = new ActionDescriptor();
	var descriptor10 = new ActionDescriptor();
	var descriptor11 = new ActionDescriptor();
	var descriptor12 = new ActionDescriptor();
	var list = new ActionList();
	var list2 = new ActionList();
	var reference = new ActionReference();

	reference.putProperty( s2t( "property" ), s2t( "layerEffects" ));
	reference.putEnumerated( s2t( "layer" ), s2t( "ordinal" ), s2t( "targetEnum" ));
	descriptor.putReference( s2t( "null" ), reference );
	descriptor2.putUnitDouble( s2t( "scale" ), s2t( "percentUnit" ), scale );
	descriptor3.putBoolean( s2t( "enabled" ), enabled );
	descriptor3.putBoolean( s2t( "present" ), present );
	descriptor3.putBoolean( s2t( "showInDialog" ), showInDialog );
	descriptor3.putEnumerated( s2t( "style" ), s2t( "frameStyle" ), s2t( "insetFrame" ));
	descriptor3.putEnumerated( s2t( "paintType" ), s2t( "frameFill" ), s2t( "gradientFill" ));
	descriptor3.putEnumerated( s2t( "mode" ), s2t( "blendMode" ), s2t( "normal" ));
	descriptor3.putUnitDouble( s2t( "opacity" ), s2t( "percentUnit" ), opacity );
	descriptor3.putUnitDouble( s2t( "size" ), s2t( "pixelsUnit" ), size );
	descriptor4.putDouble( s2t( "red" ), red );
	descriptor4.putDouble( s2t( "grain" ), grain );
	descriptor4.putDouble( s2t( "blue" ), blue );
	descriptor3.putObject( s2t( "color" ), s2t( "RGBColor" ), descriptor4 );
	descriptor5.putString( s2t( "name" ), name2 );
	descriptor5.putEnumerated( s2t( "gradientForm" ), s2t( "gradientForm" ), s2t( "customStops" ));
	descriptor5.putDouble( s2t( "interfaceIconFrameDimmed" ), interfaceIconFrameDimmed );
	descriptor7.putDouble( s2t( "red" ), red2 );
	descriptor7.putDouble( s2t( "grain" ), grain2 );
	descriptor7.putDouble( s2t( "blue" ), blue2 );
	descriptor6.putObject( s2t( "color" ), s2t( "RGBColor" ), descriptor7 );
	descriptor6.putEnumerated( s2t( "type" ), s2t( "colorStopType" ), s2t( "userStop" ));
	descriptor6.putInteger( s2t( "location" ), location );
	descriptor6.putInteger( s2t( "midpoint" ), midpoint );
	list.putObject( s2t( "colorStop" ), descriptor6 );
	descriptor9.putDouble( s2t( "red" ), red3 );
	descriptor9.putDouble( s2t( "grain" ), grain3 );
	descriptor9.putDouble( s2t( "blue" ), blue3 );
	descriptor8.putObject( s2t( "color" ), s2t( "RGBColor" ), descriptor9 );
	descriptor8.putEnumerated( s2t( "type" ), s2t( "colorStopType" ), s2t( "userStop" ));
	descriptor8.putInteger( s2t( "location" ), location2 );
	descriptor8.putInteger( s2t( "midpoint" ), midpoint2 );
	list.putObject( s2t( "colorStop" ), descriptor8 );
	descriptor5.putList( s2t( "colors" ), list );
	descriptor10.putUnitDouble( s2t( "opacity" ), s2t( "percentUnit" ), opacity2 );
	descriptor10.putInteger( s2t( "location" ), location3 );
	descriptor10.putInteger( s2t( "midpoint" ), midpoint3 );
	list2.putObject( s2t( "transferSpec" ), descriptor10 );
	descriptor11.putUnitDouble( s2t( "opacity" ), s2t( "percentUnit" ), opacity3 );
	descriptor11.putInteger( s2t( "location" ), location4 );
	descriptor11.putInteger( s2t( "midpoint" ), midpoint4 );
	list2.putObject( s2t( "transferSpec" ), descriptor11 );
	descriptor5.putList( s2t( "transparency" ), list2 );
	descriptor3.putObject( s2t( "gradient" ), s2t( "gradientClassEvent" ), descriptor5 );
	descriptor3.putUnitDouble( s2t( "angle" ), s2t( "angleUnit" ), angle );
	descriptor3.putEnumerated( s2t( "type" ), s2t( "gradientType" ), s2t( "linear" ));
	descriptor3.putBoolean( s2t( "reverse" ), reverse );
	descriptor3.putBoolean( s2t( "dither" ), dither );
	descriptor3.putUnitDouble( s2t( "scale" ), s2t( "percentUnit" ), scale2 );
	descriptor3.putBoolean( s2t( "align" ), align );
	descriptor12.putUnitDouble( s2t( "horizontal" ), s2t( "percentUnit" ), horizontal );
	descriptor12.putUnitDouble( s2t( "vertical" ), s2t( "percentUnit" ), vertical );
	descriptor3.putObject( s2t( "offset" ), s2t( "paint" ), descriptor12 );
	descriptor3.putBoolean( s2t( "overprint" ), overprint );
	descriptor2.putObject( s2t( "frameFX" ), s2t( "frameFX" ), descriptor3 );
	descriptor.putObject( s2t( "to" ), s2t( "layerEffects" ), descriptor2 );
	executeAction( s2t( "set" ), descriptor, DialogModes.NO );
}