Repository: sveltejs/svelte (JavaScript) — Bug Fix

Issue:
Delays not being applied
Think I just forgot to implement this ([REPL](https://svelte.technology/repl?version=1.19.1&gist=ab8155d6c3b0705d31c1bc1874d8d168)).

It does raise a question though — if a *bidirectional* transition has a delay, should it apply if a transition is aborted, or only for fresh transitions? I.e. if you reverse an intro half-way through, should you wait half a second before outroing, or outro immediately? I guess it would be surprising if the delay *wasn't* applied, in which case presumably we can't abort the intro until the outro starts.

Any thoughts? (This is the sort of thing I meant when I said I wanted to avoid opinions as far as possible, but sometimes you can't avoid the need to have some...)
Delays not being applied
Think I just forgot to implement this ([REPL](https://svelte.technology/repl?version=1.19.1&gist=ab8155d6c3b0705d31c1bc1874d8d168)).

It does raise a question though — if a *bidirectional* transition has a delay, should it apply if a transition is aborted, or only for fresh transitions? I.e. if you reverse an intro half-way through, should you wait half a second before outroing, or outro immediately? I guess it would be surprising if the delay *wasn't* applied, in which case presumably we can't abort the intro until the outro starts.

Any thoughts? (This is the sort of thing I meant when I said I wanted to avoid opinions as far as possible, but sometimes you can't avoid the need to have some...)


Discussion:

Resolving patch:
diff --git a/src/generators/dom/visitors/Element/addTransitions.js b/src/generators/dom/visitors/Element/addTransitions.js
--- a/src/generators/dom/visitors/Element/addTransitions.js
+++ b/src/generators/dom/visitors/Element/addTransitions.js
@@ -14,14 +14,14 @@ export default function addTransitions ( generator, block, state, node, intro, o
 		block.builders.intro.addBlock( deindent`
 			${block.component}._renderHooks.push( function () {
 				if ( !${name} ) ${name} = ${wrapTransition}( ${state.name}, ${fn}, ${snippet}, true, null );
-				${name}.run( ${name}.t, 1, function () {
+				${name}.run( true, function () {
 					${block.component}.fire( 'intro.end', { node: ${state.name} });
 				});
 			});
 		` );
 
 		block.builders.outro.addBlock( deindent`
-			${name}.run( ${name}.t, 0, function () {
+			${name}.run( false, function () {
 				${block.component}.fire( 'outro.end', { node: ${state.name} });
 				if ( --${block.alias( 'outros' )} === 0 ) ${block.alias( 'outrocallback' )}();
 				${name} = null;
@@ -49,7 +49,7 @@ export default function addTransitions ( generator, block, state, node, intro, o
 			block.builders.intro.addBlock( deindent`
 				${block.component}._renderHooks.push( function () {
 					${introName} = ${wrapTransition}( ${state.name}, ${fn}, ${snippet}, true, null );
-					${introName}.run( 0, 1, function () {
+					${introName}.run( true, function () {
 						${block.component}.fire( 'intro.end', { node: ${state.name} });
 					});
 				});
@@ -66,7 +66,7 @@ export default function addTransitions ( generator, block, state, node, intro, o
 			// group) prior to their removal from the DOM
 			block.builders.outro.addBlock( deindent`
 				${outroName} = ${wrapTransition}( ${state.name}, ${fn}, ${snippet}, false, null );
-				${outroName}.run( 1, 0, function () {
+				${outroName}.run( false, function () {
 					${block.component}.fire( 'outro.end', { node: ${state.name} });
 					if ( --${block.alias( 'outros' )} === 0 ) ${block.alias( 'outrocallback' )}();
 				});
diff --git a/src/shared/transitions.js b/src/shared/transitions.js
--- a/src/shared/transitions.js
+++ b/src/shared/transitions.js
@@ -28,7 +28,7 @@ export function generateKeyframes ( a, b, delta, duration, ease, fn, node, style
 }
 
 export function wrapTransition ( node, fn, params, intro, outgroup ) {
-	var obj = fn( node, params, intro );
+	var obj = fn( node, params );
 	var duration = obj.duration || 300;
 	var ease = obj.easing || linear;
 
@@ -40,26 +40,21 @@ export function wrapTransition ( node, fn, params, intro, outgroup ) {
 	if ( intro && obj.tick ) obj.tick( 0 );
 
 	return {
-		start: null,
-		end: null,
-		a: null,
-		b: null,
-		d: null,
-		running: false,
 		t: intro ? 0 : 1,
-		callback: null,
-		run: function ( a, b, callback ) {
-			this.a = a;
-			this.b = b;
-			this.delta = b - a;
-			this.start = window.performance.now() + ( obj.delay || 0 );
-			this.duration = duration * Math.abs( b - a );
-			this.end = this.start + this.duration;
-
-			this.callback = callback;
-
-			if ( obj.css ) {
-				generateKeyframes( this.a, this.b, this.delta, this.duration, ease, obj.css, node, style );
+		running: false,
+		program: null,
+		pending: null,
+		run: function ( intro, callback ) {
+			var program = {
+				start: window.performance.now() + ( obj.delay || 0 ),
+				intro: intro,
+				callback: callback
+			};
+
+			if ( obj.delay ) {
+				this.pending = program;
+			} else {
+				this.start( program );
 			}
 
 			if ( !this.running ) {
@@ -67,20 +62,40 @@ export function wrapTransition ( node, fn, params, intro, outgroup ) {
 				transitionManager.add( this );
 			}
 		},
+		start: function ( program ) {
+			program.a = this.t;
+			program.b = program.intro ? 1 : 0;
+			program.delta = program.b - program.a;
+			program.duration = duration * Math.abs( program.b - program.a );
+			program.end = program.start + program.duration;
+
+			if ( obj.css ) {
+				generateKeyframes( program.a, program.b, program.delta, program.duration, ease, obj.css, node, style );
+			}
+
+			this.program = program;
+			this.pending = null;
+		},
 		update: function ( now ) {
-			var p = now - this.start;
-			this.t = this.a + this.delta * ease( p / this.duration );
+			var program = this.program;
+			if ( !program ) return;
+
+			var p = now - program.start;
+			this.t = program.a + program.delta * ease( p / program.duration );
 			if ( obj.tick ) obj.tick( this.t );
 		},
 		done: function () {
-			if ( obj.tick ) obj.tick( intro ? 1 : 0 );
+			this.t = this.program.b;
+			if ( obj.tick ) obj.tick( this.t );
 			if ( obj.css ) document.head.removeChild( style );
-			this.callback();
-			this.running = false;
+			this.program.callback();
+			this.program = null;
+			this.running = !!this.pending;
 		},
 		abort: function () {
 			if ( obj.tick ) obj.tick( 1 );
 			if ( obj.css ) document.head.removeChild( style );
+			this.program = this.pending = null;
 			this.running = false;
 		}
 	};
@@ -108,16 +123,18 @@ export var transitionManager = {
 		while ( i-- ) {
 			var transition = transitionManager.transitions[i];
 
-			if ( transition.running ) {
-				if ( now >= transition.end ) {
-					transition.running = false;
-					transition.done();
-				} else if ( now > transition.start ) {
-					transition.update( now );
-				}
+			if ( transition.program && now >= transition.program.end ) {
+				transition.done();
+			}
+
+			if ( transition.pending && now >= transition.pending.start ) {
+				transition.start( transition.pending );
+			}
 
+			if ( transition.running ) {
+				transition.update( now );
 				transitionManager.running = true;
-			} else {
+			} else if ( !transition.pending ) {
 				transitionManager.transitions.splice( i, 1 );
 			}
 		}


Test patch:
diff --git a/test/runtime/samples/transition-js-delay-in-out/_config.js b/test/runtime/samples/transition-js-delay-in-out/_config.js
new file mode 100644
--- /dev/null
+++ b/test/runtime/samples/transition-js-delay-in-out/_config.js
@@ -0,0 +1,24 @@
+export default {
+	test ( assert, component, target, window, raf ) {
+		component.set({ visible: true });
+		const div = target.querySelector( 'div' );
+		assert.equal( div.foo, 0 );
+
+		raf.tick( 50 );
+		assert.equal( div.foo, 0 );
+
+		raf.tick( 150 );
+		assert.equal( div.foo, 1 );
+
+		component.set({ visible: false });
+		assert.equal( div.bar, undefined );
+
+		raf.tick( 200 );
+		assert.equal( div.bar, 1 );
+
+		raf.tick( 300 );
+		assert.equal( div.bar, 0 );
+
+		component.destroy();
+	}
+};
\ No newline at end of file
diff --git a/test/runtime/samples/transition-js-delay-in-out/main.html b/test/runtime/samples/transition-js-delay-in-out/main.html
new file mode 100644
--- /dev/null
+++ b/test/runtime/samples/transition-js-delay-in-out/main.html
@@ -0,0 +1,29 @@
+{{#if visible}}
+	<div in:foo out:bar>delayed</div>
+{{/if}}
+
+<script>
+	export default {
+		transitions: {
+			foo: function ( node, params ) {
+				return {
+					delay: 50,
+					duration: 100,
+					tick: t => {
+						node.foo = t;
+					}
+				};
+			},
+
+			bar: function ( node, params ) {
+				return {
+					delay: 50,
+					duration: 100,
+					tick: t => {
+						node.bar = t;
+					}
+				};
+			}
+		}
+	};
+</script>
\ No newline at end of file
diff --git a/test/runtime/samples/transition-js-delay/_config.js b/test/runtime/samples/transition-js-delay/_config.js
new file mode 100644
--- /dev/null
+++ b/test/runtime/samples/transition-js-delay/_config.js
@@ -0,0 +1,29 @@
+export default {
+	test ( assert, component, target, window, raf ) {
+		component.set({ visible: true });
+		const div = target.querySelector( 'div' );
+		assert.equal( div.foo, 0 );
+
+		raf.tick( 50 );
+		assert.equal( div.foo, 0 );
+
+		raf.tick( 100 );
+		assert.equal( div.foo, 0.5 );
+
+		component.set({ visible: false });
+
+		raf.tick( 125 );
+		assert.equal( div.foo, 0.75 );
+
+		raf.tick( 150 );
+		assert.equal( div.foo, 1 );
+
+		raf.tick( 175 );
+		assert.equal( div.foo, 0.75 );
+
+		raf.tick( 250 );
+		assert.equal( div.foo, 0 );
+
+		component.destroy();
+	}
+};
\ No newline at end of file
diff --git a/test/runtime/samples/transition-js-delay/main.html b/test/runtime/samples/transition-js-delay/main.html
new file mode 100644
--- /dev/null
+++ b/test/runtime/samples/transition-js-delay/main.html
@@ -0,0 +1,19 @@
+{{#if visible}}
+	<div transition:foo>delayed</div>
+{{/if}}
+
+<script>
+	export default {
+		transitions: {
+			foo: function ( node, params ) {
+				return {
+					delay: 50,
+					duration: 100,
+					tick: t => {
+						node.foo = t;
+					}
+				};
+			}
+		}
+	};
+</script>
\ No newline at end of file
diff --git a/test/runtime/samples/transition-js-dynamic-if-block-bidi/_config.js b/test/runtime/samples/transition-js-dynamic-if-block-bidi/_config.js
--- a/test/runtime/samples/transition-js-dynamic-if-block-bidi/_config.js
+++ b/test/runtime/samples/transition-js-dynamic-if-block-bidi/_config.js
@@ -11,7 +11,7 @@ export default {
 		const div = target.querySelector( 'div' );
 		assert.equal( div.foo, 0 );
 
-		raf.tick( 300 );
+		raf.tick( 75 );
 		component.set({ name: 'everybody' });
 		assert.equal( div.foo, 0.75 );
 		assert.htmlEqual( div.innerHTML, 'hello everybody!' );
@@ -19,18 +19,18 @@ export default {
 		component.set({ visible: false, name: 'again' });
 		assert.htmlEqual( div.innerHTML, 'hello everybody!' );
 
-		raf.tick( 500 );
+		raf.tick( 125 );
 		assert.equal( div.foo, 0.25 );
 
 		component.set({ visible: true });
-		raf.tick( 700 );
+		raf.tick( 175 );
 		assert.equal( div.foo, 0.75 );
 		assert.htmlEqual( div.innerHTML, 'hello again!' );
 
-		raf.tick( 800 );
+		raf.tick( 200 );
 		assert.equal( div.foo, 1 );
 
-		raf.tick( 900 );
+		raf.tick( 225 );
 
 		component.destroy();
 	}
diff --git a/test/runtime/samples/transition-js-dynamic-if-block-bidi/main.html b/test/runtime/samples/transition-js-dynamic-if-block-bidi/main.html
--- a/test/runtime/samples/transition-js-dynamic-if-block-bidi/main.html
+++ b/test/runtime/samples/transition-js-dynamic-if-block-bidi/main.html
@@ -8,7 +8,7 @@
 			foo: function ( node, params ) {
 				global.count += 1;
 				return {
-					duration: 400,
+					duration: 100,
 					tick: t => {
 						node.foo = t;
 					}