Index

Index renders a list tracked by index position. Unlike For, which tracks items by key, Index reuses DOM nodes at each position and updates their content when the item at that index changes.

Props

Prop	Type	Description
each	T[] | () => T[]	The array to iterate — static or accessor
children	(item: () => T, index: number) => JSX.Element	Render function receiving an item accessor and a static index

Note that index is a plain number (not an accessor) since the node is always at the same position.

Example

import { sig, val, set, mount, Index } from "@hedystia/view";

function ColorPalette() {
  const colors = sig(["#ff0000", "#00ff00", "#0000ff"]);

  const addColor = () => {
    const hex = "#" + Math.floor(Math.random() * 0xffffff).toString(16).padStart(6, "0");
    set(colors, [...val(colors), hex]);
  };

  return (
    <div>
      <button onClick={addColor}>Add Color</button>
      <div style={{ display: "flex", gap: "8px", marginTop: "8px" }}>
        <Index each={() => val(colors)}>
          {(color, index) => (
            <div
              style={() => ({
                width: "48px",
                height: "48px",
                backgroundColor: val(color),
                borderRadius: "4px",
              })}
              title={`Color ${index}`}
            />
          )}
        </Index>
      </div>
    </div>
  );
}

mount(ColorPalette, document.getElementById("root")!);

When to Use Index vs For

• For — best when items have unique keys and the list may be reordered. DOM nodes move with their data.
• Index — best when items are positional (e.g., rows in a grid) and the data at each index may change. DOM nodes stay in place.