dont render undefined/null attributes in SSR

src/compile/nodes/Attribute.ts

@@ -1,4 +1,4 @@
-import { escape, escapeTemplate, stringify } from '../../utils/stringify';
+import { stringify } from '../../utils/stringify';
 import addToSet from '../../utils/addToSet';
 import Component from '../Component';
 import Node from './shared/Node';
@@ -16,6 +16,7 @@ export default class Attribute extends Node {
 	name: string;
 	isSpread: boolean;
 	isTrue: boolean;
+	isConcatenated: boolean;
 	isDynamic: boolean;
 	isSynthetic: boolean;
 	shouldCache: boolean;
@@ -38,6 +39,7 @@ export default class Attribute extends Node {
 
 			this.isDynamic = true; // TODO not necessarily
 			this.shouldCache = false; // TODO does this mean anything here?
+			this.isConcatenated = false;
 		}
 
 		else {
@@ -65,6 +67,8 @@ export default class Attribute extends Node {
 					? this.chunks[0].node.type !== 'Identifier' || scope.names.has(this.chunks[0].node.name)
 					: true
 				: false;
+
+			this.isConcatenated = this.chunks.length > 1;
 		}
 	}
 
@@ -99,16 +103,4 @@ export default class Attribute extends Node {
 				? this.chunks[0].data
 				: '';
 	}
-
-	stringifyForSsr() {
-		return this.chunks
-			.map((chunk: Node) => {
-				if (chunk.type === 'Text') {
-					return escapeTemplate(escape(chunk.data).replace(/"/g, '"'));
-				}
-
-				return '${@escape(' + chunk.snippet + ')}';
-			})
-			.join('');
-	}
 }

src/compile/render-ssr/handlers/Element.ts

@@ -1,5 +1,8 @@
 import { quotePropIfNecessary, quoteNameIfNecessary } from '../../../utils/quoteIfNecessary';
 import isVoidElementName from '../../../utils/isVoidElementName';
+import Attribute from '../../nodes/Attribute';
+import Node from '../../nodes/shared/Node';
+import { escapeTemplate } from '../../../utils/stringify';
 
 // source: https://gist.github.com/ArjanSchouten/0b8574a6ad7f5065a5e7
 const boolean_attributes = new Set([
@@ -71,7 +74,7 @@ export default function(node, renderer, options) {
 				args.push(attribute.expression.snippet);
 			} else {
 				if (attribute.name === 'value' && node.name === 'textarea') {
-					textareaContents = attribute.stringifyForSsr();
+					textareaContents = stringifyAttribute(attribute);
 				} else if (attribute.isTrue) {
 					args.push(`{ ${quoteNameIfNecessary(attribute.name)}: true }`);
 				} else if (
@@ -82,18 +85,18 @@ export default function(node, renderer, options) {
 					// a boolean attribute with one non-Text chunk
 					args.push(`{ ${quoteNameIfNecessary(attribute.name)}: ${attribute.chunks[0].snippet} }`);
 				} else {
-					args.push(`{ ${quoteNameIfNecessary(attribute.name)}: \`${attribute.stringifyForSsr()}\` }`);
+					args.push(`{ ${quoteNameIfNecessary(attribute.name)}: \`${stringifyAttribute(attribute)}\` }`);
 				}
 			}
 		});
 
 		openingTag += "${@spread([" + args.join(', ') + "])}";
 	} else {
-		node.attributes.forEach((attribute: Node) => {
+		node.attributes.forEach((attribute: Attribute) => {
 			if (attribute.type !== 'Attribute') return;
 
 			if (attribute.name === 'value' && node.name === 'textarea') {
-				textareaContents = attribute.stringifyForSsr();
+				textareaContents = stringifyAttribute(attribute);
 			} else if (attribute.isTrue) {
 				openingTag += ` ${attribute.name}`;
 			} else if (
@@ -105,9 +108,14 @@ export default function(node, renderer, options) {
 				openingTag += '${' + attribute.chunks[0].snippet + ' ? " ' + attribute.name + '" : "" }';
 			} else if (attribute.name === 'class' && classExpr) {
 				addClassAttribute = false;
-				openingTag += ` class="\${[\`${attribute.stringifyForSsr()}\`, ${classExpr}].join(' ').trim() }"`;
+				openingTag += ` class="\${[\`${stringifyAttribute(attribute)}\`, ${classExpr}].join(' ').trim() }"`;
+			} else if (attribute.isConcatenated || !attribute.isDynamic) {
+				openingTag += ` ${attribute.name}="${stringifyAttribute(attribute)}"`;
 			} else {
-				openingTag += ` ${attribute.name}="${attribute.stringifyForSsr()}"`;
+				const { name } = attribute;
+				const { snippet } = attribute.chunks[0];
+
+				openingTag += '${(v => v == null ? "" : ` ' + name + '=${' + snippet + '}`)(' + snippet + ')}';
 			}
 		});
 	}
@@ -130,3 +138,15 @@ export default function(node, renderer, options) {
 		renderer.append(`</${node.name}>`);
 	}
 }
+
+function stringifyAttribute(attribute: Attribute) {
+	return attribute.chunks
+		.map((chunk: Node) => {
+			if (chunk.type === 'Text') {
+				return escapeTemplate(escape(chunk.data).replace(/"/g, '&quot;'));
+			}
+
+			return '${@escape(' + chunk.snippet + ')}';
+		})
+		.join('');
+}

src/shared/dom.js

@@ -82,7 +82,7 @@ export function removeListener(node, event, handler) {
 }
 
 export function setAttribute(node, attribute, value) {
-	if (value == null) removeAttribute(node, attribute);
+	if (value == null) node.removeAttribute(attribute);
 	else node.setAttribute(attribute, value);
 }
 
@@ -104,14 +104,10 @@ export function setCustomElementData(node, prop, value) {
 	} else if (value) {
 		setAttribute(node, prop, value);
 	} else {
-		removeAttribute(node, prop);
+		node.removeAttribute(prop);
 	}
 }
 
-export function removeAttribute(node, attribute) {
-	node.removeAttribute(attribute);
-}
-
 export function setXlinkAttribute(node, attribute, value) {
 	node.setAttributeNS('http://www.w3.org/1999/xlink', attribute, value);
 }

test/runtime/samples/set-undefined-attr/_config.js

@@ -1,5 +1,5 @@
 export default {
-	'skip-ssr': true,
+	html: '<div></div>',
 
-	html: '<div></div>'
+	ssrHtml: '<div foo=1></div>'
 };