Interpolation Functions
Customize how tweened stores interpolate between complex values like colors and arrays.
Interpolation Functions is a free Sveltejs Academy lesson on CoddyKit. This is lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Sveltejs Academy learning path, and your progress syncs across the web and the CoddyKit app. The Sveltejs Academy course includes 4 lessons in total.
Custom Interpolation
Tweened and spring can animate non-numeric values with a custom interpolate function.
Function Signature
The interpolate function takes start and end values and returns a function that maps progress to interpolated value.
function lerp(a, b) { return (t) => a + (b - a) * t; }Pass to Tweened
Provide your function in the options.
const p = tweened(0, { interpolate: lerp });Color Interpolation
Use libraries like d3-interpolate to interpolate between colors.
Array Interpolation
Interpolate per-element for arrays of numbers, like SVG path coordinates.
Object Interpolation
Default behavior interpolates numeric properties; supply custom for non-numeric ones.
SVG Paths
Animate SVG path strings by interpolating their coordinates.
Tweened Strings
Strings (other than colors) usually need a custom function to interpolate meaningfully.
Why Custom
Custom interpolation unlocks creative animations of complex data shapes.
Combine With easing
Easing shapes the curve; interpolation maps the value space. They work together.
Performance
Keep interpolation cheap; it runs every animation frame.
Quick Check
What does interpolate do?
Recap
Custom interpolate functions extend motion stores to colors, paths, and any value with a meaningful "between".
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Frequently Asked Questions
Is the “Interpolation Functions” lesson free?
Yes — the full text of “Interpolation Functions” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Sveltejs Academy course, upgrade to CoddyKit PRO. The Sveltejs Academy course includes 4 lessons in total.
What will I learn in “Interpolation Functions”?
Customize how tweened stores interpolate between complex values like colors and arrays. You practise Sveltejs Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Sveltejs Academy?
No prior experience is required. Sveltejs Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.
How long does the “Interpolation Functions” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Sveltejs Academy lesson?
Yes. Every Sveltejs Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- The spring() Store: Physics-Based Animation
- The tweened() Store: Duration and Easing
- Interpolation Functions
- Animating SVG Paths with Motion