Reactive Dependencies and Ordering
Understand how Svelte tracks dependencies and orders reactive statements.
Reactive Dependencies and Ordering is a free Sveltejs Academy lesson on CoddyKit — lesson 2 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, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Static Analysis
The compiler scans each $: statement for references to reactive variables. Those become its dependencies.
Implicit Dependencies
Indirect references (through functions) may not be detected. Reference variables directly when possible.
Function Calls
If a function returns a value derived from reactive variables, pass them in for tracking.
$: total = sum(items, qty); // items and qty are trackedTopological Order
Svelte orders statements so dependencies run first. $: y = x * 2; $: z = y * 3 works as expected.
Dependency Cycles
Avoid creating cycles between reactive statements. They can cause infinite updates.
Conditional Dependencies
If a variable is referenced only inside an if, it may not be tracked when the condition is false.
Array/Object Mutation
Mutation does not trigger updates. Reassign to refresh dependencies.
Across Components
Reactive statements track only same-component variables. Use stores to span components.
Common Pitfall
Async work inside reactive statements may re-trigger before old work finishes. Cancel or guard.
Watching Multiple Values
To run an effect when several values change, reference them all on the right side.
Debugging
Add console logs inside $: to see when statements run during development.
Quick Check
What determines dependencies of a reactive statement?
Recap
Dependencies are determined by static analysis of the statement's references. Statements run in topological dependency order.
Frequently asked questions
Is the “Reactive Dependencies and Ordering” lesson free?
Yes — the full text of “Reactive Dependencies and Ordering” is free to read here on the web, and the Sveltejs Academy course includes 4 lessons in total. 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.
What will I learn in “Reactive Dependencies and Ordering”?
Understand how Svelte tracks dependencies and orders reactive statements. 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; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Reactive Dependencies and Ordering” 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
- Reactive Statements: $: block
- Reactive Dependencies and Ordering
- When to Use Stores vs Local State
- Avoiding Stale Closures