reference

Sessions

Session helpers tell you when London, New York, or the trading day opens and closes — so you can key logic off session boundaries instead of raw clock math.

Indicators, definitions, and studies each expose a slightly different session API for the same idea. Use this when your setup is session-based (opens, overlaps, RTH vs ETH).

Indicator — isStart

if (ctx.session.isStart("london")) {
  ctx.mark("ln_open", { price: ctx.open, text: "LN", time: ctx.time });
}

Modes: consistent, daily, weekly, monthly, london, newyork, tokyo, sydney.

Definition — session object

export function onBar(ctx) {
  const s = ctx.session({ /* SessionOpts — see IntelliSense */ });
  if (s.didOpen) {
    ctx.emit("session_open", { key: s.key }, {
      label: `Open ${s.key}`,
      timeStart: s.start,
      price: ctx.open,
    });
  }
}

Common fields: key, start, end, isOpen, didOpen, didClose, prev.

Study — key / bounds / bucket

ctx.session.key(t);
ctx.session.boundsOf(t);
ctx.session.bucket(t, "london");

Use buckets with scopeEvent / indexedBy when tables or pins are session-scoped.

Common mistakes

Assuming New York session equals exchange RTH without checking opts
Emitting once-per-session logic without definition oncePer
Using session helpers on weekly charts without runOn limits

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