sveltejs · andirady · Nov 14, 2021 · Nov 14, 2021 · Dec 18, 2021 · Jan 29, 2022
diff --git a/src/compiler/compile/nodes/Body.ts b/src/compiler/compile/nodes/Body.ts
@@ -1,6 +1,7 @@
 import Node from './shared/Node';
 import EventHandler from './EventHandler';
 import Action from './Action';
+import Class from './Class';
 import Component from '../Component';
 import TemplateScope from './shared/TemplateScope';
 import { Element } from '../../interfaces';
@@ -9,6 +10,7 @@ export default class Body extends Node {
 	type: 'Body';
 	handlers: EventHandler[] = [];
 	actions: Action[] = [];
+	classes: Class[] = [];
 
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: Element) {
 		super(component, parent, scope, info);
@@ -18,6 +20,8 @@ export default class Body extends Node {
 				this.handlers.push(new EventHandler(component, this, scope, node));
 			} else if (node.type === 'Action') {
 				this.actions.push(new Action(component, this, scope, node));
+			} else if (node.type === 'Class') {
+				this.classes.push(new Class(component, this, scope, node));
 			} else {
 				// TODO there shouldn't be anything else here...
 			}

diff --git a/src/compiler/compile/render_dom/wrappers/Body.ts b/src/compiler/compile/render_dom/wrappers/Body.ts
@@ -1,25 +1,66 @@
 import Block from '../Block';
 import Wrapper from './shared/Wrapper';
-import { x } from 'code-red';
+import { b, x } from 'code-red';
 import Body from '../../nodes/Body';
-import { Identifier } from 'estree';
+import { Node, Identifier } from 'estree';
 import EventHandler from './Element/EventHandler';
 import add_event_handlers from './shared/add_event_handlers';
 import { TemplateNode } from '../../../interfaces';
 import Renderer from '../Renderer';
 import add_actions from './shared/add_actions';
+import is_dynamic from './shared/is_dynamic';
 
 export default class BodyWrapper extends Wrapper {
 	node: Body;
 	handlers: EventHandler[];
+	class_dependencies: string[];
 
 	constructor(renderer: Renderer, block: Block, parent: Wrapper, node: TemplateNode) {
 		super(renderer, block, parent, node);
 		this.handlers = this.node.handlers.map(handler => new EventHandler(handler, this));
+		this.class_dependencies = [];
+	}
+
+	add_classes(block: Block) {
+		this.node.classes.forEach(class_directive => {
+			const { expression, name } = class_directive;
+			let snippet: Node | string;
+			let dependencies: Set<string>;
+			if (expression) {
+				snippet = expression.manipulate(block);
+				dependencies = expression.dependencies;
+			} else {
+				snippet = name;
+				dependencies = new Set([name]);
+			}
+			const updater = b`@toggle_class(@_document.body, "${name}", ${snippet});`;
+
+			block.chunks.hydrate.push(updater);
+
+			if ((dependencies && dependencies.size > -1) || this.class_dependencies.length) {
+				const all_dependencies = this.class_dependencies.concat(...dependencies);
+				const condition = block.renderer.dirty(all_dependencies);
+
+				// If all of the dependencies are non-dynamic (don't get updated) then there is no reason
+				// to add an updater for this.
+				const any_dynamic_dependencies = all_dependencies.some((dep) => {
+					const variable = this.renderer.component.var_lookup.get(dep);
+					return !variable || is_dynamic(variable);
+				});
+				if (any_dynamic_dependencies) {
+					block.chunks.update.push(b`
+                    if (${condition}) {
+                        ${updater}
+                    }
+                `);
+				}
+			}
+		});
 	}
 
 	render(block: Block, _parent_node: Identifier, _parent_nodes: Identifier) {
 		add_event_handlers(block, x`@_document.body`, this.handlers);
 		add_actions(block, x`@_document.body`, this.node.actions);
+		this.add_classes(block);
 	}
 }
diff --git a/test/runtime/samples/class-body-boolean/_config.js b/test/runtime/samples/class-body-boolean/_config.js
@@ -0,0 +1,3 @@
+export default {
+	html: '<body class="one"></body>'
+};
diff --git a/test/runtime/samples/class-body-boolean/main.svelte b/test/runtime/samples/class-body-boolean/main.svelte
@@ -0,0 +1 @@
+<svelte:body class:one={true} />
diff --git a/test/runtime/samples/class-body-shortcut/_config.js b/test/runtime/samples/class-body-shortcut/_config.js
@@ -0,0 +1,16 @@
+export default {
+	props: {
+		foo: true,
+		bar: true
+	},
+
+	html: '<body class="foo bar"></body>',
+
+	test({ assert, component, target }) {
+		component.foo = false;
+
+		assert.htmlEqual(target.innerHTML, `
+			<body class="bar"></body>
+		`);
+	}
+};
diff --git a/test/runtime/samples/class-body-shortcut/main.svelte b/test/runtime/samples/class-body-shortcut/main.svelte
@@ -0,0 +1,7 @@
+<script>
+	export let foo;
+	export let bar;
+	export let unused;
+</script>
+
+<svelte:body class:foo class:bar class:unused />