omit falsy boolean attributes

src/compiler/compile/render_ssr/handlers/Element.ts

@@ -140,7 +140,7 @@ export default function(node: Element, renderer: Renderer, options: RenderOption
 			} else if (attribute.chunks.length === 1 && attribute.chunks[0].type !== 'Text') {
 				const { name } = attribute;
 				const snippet = snip(attribute.chunks[0]);
-				opening_tag += '${@add_attribute("' + name + '", ' + snippet + ')}';
+				opening_tag += '${@add_attribute("' + name + '", ' + snippet + ', ' + (boolean_attributes.has(name) ? 1 : 0) + ')}';
 			} else {
 				opening_tag += ` ${attribute.name}="${stringify_attribute(attribute, true)}"`;
 			}
@@ -164,7 +164,7 @@ export default function(node: Element, renderer: Renderer, options: RenderOption
 			node_contents = '${(' + snippet + ') || ""}';
 		} else {
 			const snippet = snip(expression);
-			opening_tag += '${@add_attribute("' + name + '", ' + snippet + ')}';
+			opening_tag += '${@add_attribute("' + name + '", ' + snippet + ', 1)}';
 		}
 	});
 

src/runtime/internal/ssr.ts

@@ -133,9 +133,9 @@ export function get_store_value<T>(store: Readable<T>): T | undefined {
 	return value;
 }
 
-export function add_attribute(name, value) {
+export function add_attribute(name, value, boolean) {
-	if (value == null) return '';
+	if (value == null || (boolean && !value)) return '';
-	return ` ${name}${value === true ? '' : `=${typeof value === 'string' ? JSON.stringify(value) : `"${value}"`}`}`;
+	return ` ${name}${value === true ? '' : `=${typeof value === 'string' ? JSON.stringify(escape(value)) : `"${value}"`}`}`;
 }
 
 export function add_classes(classes) {