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108 lines
4.3 KiB
Markdown
108 lines
4.3 KiB
Markdown
---
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name: gsap-timeline
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description: Official GSAP skill for timelines — gsap.timeline(), position parameter, nesting, playback. Use when sequencing animations, choreographing keyframes, or when the user asks about animation sequencing, timelines, or animation order (in GSAP or when recommending a library that supports timelines).
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license: MIT
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---
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# GSAP Timeline
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## When to Use This Skill
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Apply when building multi-step animations, coordinating several tweens in sequence or parallel, or when the user asks about timelines, sequencing, or keyframe-style animation in GSAP.
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**Related skills:** For single tweens and eases use **gsap-core**; for scroll-driven timelines use **gsap-scrolltrigger**; for React use **gsap-react**.
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## Creating a Timeline
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```javascript
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const tl = gsap.timeline();
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tl.to(".a", { x: 100, duration: 1 })
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.to(".b", { y: 50, duration: 0.5 })
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.to(".c", { opacity: 0, duration: 0.3 });
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```
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By default, tweens are **appended** one after another. Use the **position parameter** to place tweens at specific times or relative to other tweens.
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## Position Parameter
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Third argument (or position property in vars) controls placement:
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- **Absolute**: `1` — start at 1 second.
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- **Relative (default)**: `"+=0.5"` — 0.5s after end; `"-=0.2"` — 0.2s before end.
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- **Label**: `"labelName"` — at that label; `"labelName+=0.3"` — 0.3s after label.
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- **Placement**: `"<"` — start when recently-added animation starts; `">"` — start when recently-added animation ends (default); `"<0.2"` — 0.2s after recently-added animation start.
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Examples:
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```javascript
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tl.to(".a", { x: 100 }, 0); // at 0
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tl.to(".b", { y: 50 }, "+=0.5"); // 0.5s after last end
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tl.to(".c", { opacity: 0 }, "<"); // same start as previous
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tl.to(".d", { scale: 2 }, "<0.2"); // 0.2s after previous start
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```
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## Timeline Defaults
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Pass defaults into the timeline so all child tweens inherit:
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```javascript
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const tl = gsap.timeline({ defaults: { duration: 0.5, ease: "power2.out" } });
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tl.to(".a", { x: 100 }).to(".b", { y: 50 }); // both use 0.5s and power2.out
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```
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## Timeline Options (constructor)
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- **paused: true** — create paused; call `.play()` to start.
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- **repeat**, **yoyo** — same as tweens; apply to whole timeline.
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- **onComplete**, **onStart**, **onUpdate** — timeline-level callbacks.
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- **defaults** — vars merged into every child tween.
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## Labels
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Add and use labels for readable, maintainable sequencing:
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```javascript
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tl.addLabel("intro", 0);
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tl.to(".a", { x: 100 }, "intro");
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tl.addLabel("outro", "+=0.5");
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tl.to(".b", { opacity: 0 }, "outro");
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tl.play("outro"); // start from "outro"
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tl.tweenFromTo("intro", "outro"); // pauses the timeline and returns a new Tween that animates the timeline's playhead from intro to outro with no ease.
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```
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## Nesting Timelines
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Timelines can contain other timelines.
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```javascript
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const master = gsap.timeline();
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const child = gsap.timeline();
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child.to(".a", { x: 100 }).to(".b", { y: 50 });
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master.add(child, 0);
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master.to(".c", { opacity: 0 }, "+=0.2");
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```
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## Controlling Playback
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- **tl.play()** / **tl.pause()**
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- **tl.reverse()** / **tl.progress(1)** then **tl.reverse()**
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- **tl.restart()** — from start.
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- **tl.time(2)** — seek to 2 seconds.
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- **tl.progress(0.5)** — seek to 50%.
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- **tl.kill()** — kill timeline and (by default) its children.
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## Official GSAP Best practices
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- ✅ Prefer timelines for sequencing
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- ✅ Use the **position parameter** (third argument) to place tweens at specific times or relative to labels.
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- ✅ Add **labels** with `addLabel()` for readable, maintainable sequencing.
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- ✅ Pass **defaults** into the timeline constructor so child tweens inherit duration, ease, etc.
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- ✅ Put ScrollTrigger on the timeline (or top-level tween), not on tweens inside a timeline.
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## Do Not
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- ❌ Chain animations with **delay** when a **timeline** can sequence them; prefer `gsap.timeline()` and the position parameter for multi-step animation.
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- ❌ Forget to pass **defaults** (e.g. `defaults: { duration: 0.5, ease: "power2.out" }`) when many child tweens share the same duration or ease.
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- ❌ Forget that **duration** on the timeline constructor is not the same as tween duration; timeline “duration” is determined by its children.
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- ❌ Nest animations that contain a ScrollTrigger; ScrollTriggers should only be on top-level Tweens/Timelines.
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