Variables & logic

Every scene has a ctx — a plain JavaScript object that holds game state. You read it with ${...} interpolation and write it with <script> blocks or inline [exec] blocks.

Set state on scene entry

A <script> block runs once, before the body plays:

---
id: intro
---

<script>
ctx.player = { name: "Ada", gold: 80 };
ctx.visited = false;
</script>

:: Narrator :: Hello, ${player.name}.

Interpolate values in text

Inline ${expression} reads from ctx:

:: Narrator :: You carry ${player.gold} gold.

Expressions are real JavaScript — ${player.gold + 10}, ${inventory.includes("sword") ? "armed" : "unarmed"}, etc.

Branch on conditions

:::if{cond="player.gold >= 50"}
:: Merchant :: Browse my wares?
:::elseif{cond="player.gold > 0"}
:: Merchant :: You've got some coin. Here's the bargain bin.
:::else
:: Merchant :: Come back when your purse is heavier.
:::

Conditions are evaluated at runtime, not parse time. Reference anything on ctx.

Mutate mid-scene

Use [exec] ... [/exec] to run logic between lines without breaking flow:

:: Narrator :: You step on a pressure plate.

[exec]
ctx.trapTriggered = true;
ctx.hp -= 10;
[/exec]

:: Narrator :: A dart whistles past. Hp: ${hp}.

Try it live

Security note

All user expressions run through new Function(ctx, "return (" + expr + ")"). Kata never uses eval(). The context argument list is explicit and blocked globals are shadowed. See the sandbox reference for the full list.

Next: Audio & visuals →