CORRECT001 · Keyed each block

Severity: warning · Category: correctness

What it checks

Flags an {#each} block with no key. Checked by static (CLI) analysis of every .svelte component under src/. Two shapes are ignored:

• A constant inline array literal ({#each [1, 2, 3] as n}) — it has a fixed length and never reorders, so a key cannot help.
• An itemless each ({#each { length: 8 }, i}, the “render N times” pattern) — there is no item identity to key on; the only possible key is the index itself, which is a no-op.

Why it matters

Without a key, when the list reorders or items are inserted/removed, Svelte adds/removes nodes at the end and rewrites the data of the DOM nodes in between — so element state (focus, inputs, transitions) sticks to positions instead of items, and extra work is done. A key lets Svelte insert, move, and delete the right nodes instead.

How to fix

{#each items as item (item.id)}
  <li>{item.name}</li>
{/each}