CustomExportSizes.sketchplugin

// (command shift a)

if (selection.length() > 0){
	for (var i=0; i < selection.length(); i++) {
		addExportSizes(selection[i]);
	}

	[doc showMessage:"Export Options Added"];
} else {
	var app = [NSApplication sharedApplication];
	[app displayDialog:"Anything selected :(" withTitle:"Exportabler"];
}

function addExportSizes(layer) {
	var iOSExportData = [{"format": "png", "scale": 0.5, "suffix": ""},
						 {"format": "png", "scale": 1, "suffix": "@2x"},
						 {"format": "png", "scale": 1.5, "suffix": "@3x"},
						 {"format": "png", "scale": 0.5, "suffix": "_mdpi"},
						 {"format": "png", "scale": 0.75, "suffix": "_hdpi"},
						 {"format": "png", "scale": 1, "suffix": "_xhdpi"},
						 {"format": "png", "scale": 1.5, "suffix": "_xxhdpi"}];

	var export_options = [layer exportOptions];
	var export_sizes = [export_options sizes];

	while ([export_sizes count] > 0) {
		[[export_sizes firstObject] remove]
	}

	for (var i = 0; i < iOSExportData.length; i++) {
		var size_data = iOSExportData[i];
		var size = [[layer exportOptions] addExportSize];
		[size setFormat:size_data.format];
		[size setScale:size_data.scale];
		[size setName:size_data.suffix];
	}

	[[doc currentPage] deselectAllLayers];
	[layer select:true byExpandingSelection:true];
}