Adds the class directive

src/compile/nodes/Class.ts

@@ -0,0 +1,18 @@
+import Node from './shared/Node';
+import Expression from './shared/Expression';
+
+export default class Class extends Node {
+	type: 'Class';
+	name: string;
+	expression: Expression;
+
+	constructor(compiler, parent, scope, info) {
+		super(compiler, parent, scope, info);
+
+		this.name = info.name;
+
+		this.expression = info.expression
+			? new Expression(compiler, this, scope, info.expression)
+			: null;
+	}
+}

src/compile/nodes/Element.ts

@@ -15,6 +15,7 @@ import EventHandler from './EventHandler';
 import Transition from './Transition';
 import Animation from './Animation';
 import Action from './Action';
+import Class from './Class';
 import Text from './Text';
 import * as namespaces from '../../utils/namespaces';
 import mapChildren from './shared/mapChildren';
@@ -68,6 +69,8 @@ export default class Element extends Node {
 	attributes: Attribute[];
 	actions: Action[];
 	bindings: Binding[];
+	classes: Class[];
+	classDependencies: string[];
 	handlers: EventHandler[];
 	intro?: Transition;
 	outro?: Transition;
@@ -90,6 +93,8 @@ export default class Element extends Node {
 		this.attributes = [];
 		this.actions = [];
 		this.bindings = [];
+		this.classes = [];
+		this.classDependencies = [];
 		this.handlers = [];
 
 		this.intro = null;
@@ -144,6 +149,10 @@ export default class Element extends Node {
 					this.bindings.push(new Binding(compiler, this, scope, node));
 					break;
 
+				case 'Class':
+					this.classes.push(new Class(compiler, this, scope, node));
+					break;
+
 				case 'EventHandler':
 					this.handlers.push(new EventHandler(compiler, this, scope, node));
 					break;
@@ -228,6 +237,13 @@ export default class Element extends Node {
 			block.addDependencies(binding.value.dependencies);
 		});
 
+		this.classes.forEach(classDir => {
+			this.parent.cannotUseInnerHTML();
+			if (classDir.expression) {
+				block.addDependencies(classDir.expression.dependencies);
+			}
+		});
+
 		this.handlers.forEach(handler => {
 			this.parent.cannotUseInnerHTML();
 			block.addDependencies(handler.dependencies);
@@ -403,6 +419,7 @@ export default class Element extends Node {
 		this.addTransitions(block);
 		this.addAnimation(block);
 		this.addActions(block);
+		this.addClasses(block);
 
 		if (this.initialUpdate) {
 			block.builders.mount.addBlock(this.initialUpdate);
@@ -584,6 +601,9 @@ export default class Element extends Node {
 		}
 
 		this.attributes.forEach((attribute: Attribute) => {
+			if (attribute.name === 'class' && attribute.isDynamic) {
+				this.classDependencies.push(...attribute.dependencies);
+			}
 			attribute.render(block);
 		});
 	}
@@ -867,6 +887,26 @@ export default class Element extends Node {
 		});
 	}
 
+	addClasses(block: Block) {
+		this.classes.forEach(classDir => {
+			const { expression: { snippet, dependencies}, name } = classDir;
+			const updater = `@toggleClass(${this.var}, "${name}", ${snippet});`;
+
+			block.builders.hydrate.addLine(updater);
+
+			if ((dependencies && dependencies.size > 0) || this.classDependencies.length) {
+				const allDeps = this.classDependencies.concat(...dependencies);
+				const deps = allDeps.map(dependency => `changed.${dependency}`).join(' || ');
+				const condition = allDeps.length > 1 ? `(${deps})` : deps;
+
+				block.builders.update.addConditional(
+					condition,
+					updater
+				);
+			}
+		});
+	}
+
 	getStaticAttributeValue(name: string) {
 		const attribute = this.attributes.find(
 			(attr: Attribute) => attr.type === 'Attribute' && attr.name.toLowerCase() === name
@@ -937,6 +977,13 @@ export default class Element extends Node {
 			appendTarget.slots[slotName] = '';
 		}
 
+		const classExpr = this.classes.map((classDir: Class) => {
+			const { expression: { snippet }, name } = classDir;
+			return `${snippet} ? "${name}" : ""`;
+		}).join(', ');
+
+		let addClassAttribute = classExpr ? true : false;
+
 		if (this.attributes.find(attr => attr.isSpread)) {
 			// TODO dry this out
 			const args = [];
@@ -977,12 +1024,19 @@ export default class Element extends Node {
 				) {
 					// a boolean attribute with one non-Text chunk
 					openingTag += '${' + attribute.chunks[0].snippet + ' ? " ' + attribute.name + '" : "" }';
+				} else if (attribute.name === 'class' && classExpr) {
+					addClassAttribute = false;
+					openingTag += ` class="\${ [\`${attribute.stringifyForSsr()}\`, ${classExpr} ].join(' ') }"`;
 				} else {
 					openingTag += ` ${attribute.name}="${attribute.stringifyForSsr()}"`;
 				}
 			});
 		}
 
+		if (addClassAttribute) {
+			openingTag += ` class="\${ [${classExpr}].join(' ') }"`;
+		}
+
 		openingTag += '>';
 
 		compiler.target.append(openingTag);

src/parse/read/directives.ts

@@ -81,6 +81,15 @@ const DIRECTIVES: Record<string, {
 		error: 'Data passed to actions must be an identifier (e.g. `foo`), a member expression ' +
 			'(e.g. `foo.bar` or `foo[baz]`), a method call (e.g. `foo()`), or a literal (e.g. `true` or `\'a string\'`'
 	},
+
+	Class: {
+		names: ['class'],
+		attribute(start, end, type, name, expression) {
+			return { start, end, type, name, expression };
+		},
+		allowedExpressionTypes: ['*'],
+		error: 'Data passed to class directives must be an expression'
+	},
 };
 
 

src/shared/dom.js

@@ -238,4 +238,8 @@ export function addResizeListener(element, fn) {
 			element.removeChild(object);
 		}
 	};
-}
+}
+
+export function toggleClass(element, name, toggle) {
+	element.classList.toggle(name, Boolean(toggle));
+}

src/validate/html/validateComponent.ts

@@ -25,11 +25,11 @@ export default function validateComponent(
 		if (attribute.type === 'Ref') {
 			if (!isValidIdentifier(attribute.name)) {
 				const suggestion = attribute.name.replace(/[^_$a-z0-9]/ig, '_').replace(/^\d/, '_$&');
-				
+
 				validator.error(attribute, {
 					code: `invalid-reference-name`,
 					message: `Reference name '${attribute.name}' is invalid — must be a valid identifier such as ${suggestion}`
-				});	
+				});
 			} else {
 				if (!refs.has(attribute.name)) refs.set(attribute.name, []);
 				refs.get(attribute.name).push(node);
@@ -49,6 +49,11 @@ export default function validateComponent(
 				code: `invalid-action`,
 				message: `Actions can only be applied to DOM elements, not components`
 			});
+		} else if (attribute.type === 'Class') {
+			validator.error(attribute, {
+				code: `invalid-class`,
+				message: `Classes can only be applied to DOM elements, not components`
+			});
 		}
 	});
 }

test/runtime/samples/class-boolean/_config.js

@@ -0,0 +1,3 @@
+export default {
+	html: `<div class="one"></div>`
+};

test/runtime/samples/class-boolean/main.html

@@ -0,0 +1 @@
+<div class:one="true"></div>

test/runtime/samples/class-helper/_config.js

@@ -0,0 +1,14 @@
+export default {
+	data: {
+		user: { active: true }
+	},
+	html: `<div class="active"></div>`,
+
+	test ( assert, component, target, window ) {
+		component.set({ user: { active: false }});
+
+		assert.htmlEqual( target.innerHTML, `
+			<div class></div>
+		` );
+	}
+};

test/runtime/samples/class-helper/main.html

@@ -0,0 +1,11 @@
+<div class:active="isActive(user)"></div>
+
+<script>
+export default {
+  helpers: {
+    isActive(user) {
+      return user.active;
+    }
+  }
+}
+</script>

test/runtime/samples/class-with-attribute/_config.js

@@ -0,0 +1,3 @@
+export default {
+	html: `<div class="one two three"></div>`
+};

test/runtime/samples/class-with-attribute/main.html

@@ -0,0 +1 @@
+<div class="one" class:two="true" class:three="true"></div>

test/runtime/samples/class-with-dynamic-attribute/_config.js

@@ -0,0 +1,14 @@
+export default {
+	data: {
+		myClass: 'one two'
+	},
+	html: `<div class="one two three"></div>`,
+
+	test ( assert, component, target, window ) {
+		component.set({ myClass: 'one' });
+
+		assert.htmlEqual( target.innerHTML, `
+			<div class="one three"></div>
+		` );
+	}
+};

test/runtime/samples/class-with-dynamic-attribute/main.html

@@ -0,0 +1 @@
+<div class="{ myClass }" class:three="true"></div>