useServerStateOnce

useServerStateOnce reads a value the server owns as the component builds and subscribes to nothing: the panel shows the value as it was when it opened.

useServerStateOnce(ref: ServerRef): Int
useServerStateOnce(body: () => Int): Int
useServerStateOnce(body: () => Boolean): Boolean

Reference

useServerStateOnce(ref)

src/once.ts2

export const PoisonThenAndNow = (): Component => {
  const atOpen = useServerStateOnce(Varps.POISON);
  const now = useServerState(Varps.POISON);

Parameters

• ref: A Varps.*, Varbits.* or Skills.* reference, as for useServerState.

Returns

The value at build time, typed as the reference says — an Int, or the type a variable is declared to hold.

useServerStateOnce(body)

The second form takes an arrow — useServerStateOnce(() => tierFacts(tier)) — for a value computed from several reads at build time.

Parameters

• body: An expression. Every read inside it is untracked — a variable, a skill, a cell, and everything a called function reads. It need not be a single call.

Returns

The expression’s value at build time.

Caveats

• It re-reads when the component is rebuilt, e.g. the interface reopens. A setter, new props or another read’s redraw do not re-read it. A prop the body read is the prop at build time.
• There is no setter. If the panel needs its own editable copy, seed a cell: useState(useServerStateOnce(V)).
• A seeded cell with its setter dropped is refused (TS2E239). Drop the useState and use the value.
• Inside a render body only (TS2E236). Write useServerState there.
• No subscribing hook inside the body (TS2E237). useState, useWatch, useDerived, useInventory, useOnResize, useRerenderOn and a nested once are refused. A useServerState inside the body is allowed.
• Not inside a .map() row (TS2E238). Make the row a component.

refused/use-server-state-once.ts2

  const [poison] = useState(useServerStateOnce(Varps.POISON));      // no setter: drop the useState

Usage

Showing a value as it was when the panel opened

src/once.ts2

      <Reading label="Poison on open" value={`${atOpen}`} color={Colors.WHITE} y={0} />
      <Reading label="Poison now" value={`${now}`} color={now === atOpen ? Colors.WHITE : Colors.GREEN} y={ROW_H} />

Seeding a cell

src/once.ts2

export const StaminaChoice = (): Component => {
  const [stamina, setStamina] = useState(useServerStateOnce(Varbits.STAMINA_ACTIVE));

A bar that remembers where the fight began

src/idiomatic.ts2

  const maxAtOpen = useServerStateOnce(HudVarbits.MAX_HP);

Troubleshooting

The value never updates

If the panel should follow the value, read it with useServerState.

The value updated when I did not expect it to

Something rebuilt the component.

The compiler refuses my seeded cell

You dropped the setter. If nothing will ever write the cell, you do not need one: use the read-once value directly.