feature

onBar

onBar is the function Chartnaut calls once per bar for an indicator — this is where you read price, update memory, and plot values.

Bar fields, accum, drawings, MTF, and deps are documented in Shared runtime; this page is the checklist for wiring them inside an indicator’s onBar.

Signature

function onBar(ctx: ScriptedCtx): void

Checklist

Read ctx.params from inputs.
Keep state in ctx.accum.
Emit with ctx.plot / mark / … to declared output.*.
Optional: security / tf, session.isStart, ctx.indicators.

Example

meta({ shortName: "EMA Cross", kind: "overlay" });
const length = input.number({ id: "length", label: "Length", default: 20, min: 1 });
const emaLine = output.line({ id: "ema", color: "#2196f3" });
output.markers({ id: "cross_up", on: emaLine, color: "#26a69a" });
layout(tab({ id: "main", title: "Main" }, section({ id: "p", title: "Parameters" }, length)));

function onBar(ctx) {
  const k = 2 / (ctx.params.length + 1);
  const ema = ctx.accum("ema", null, (prev) =>
    prev == null ? ctx.close : prev + k * (ctx.close - prev)
  );
  ctx.plot("ema", ema);

  const prevClose = ctx.accum("prevClose", null, () => ctx.close);
  const prevEma = ctx.accum("prevEma", null, () => ema);
  if (prevClose != null && prevEma != null && prevClose <= prevEma && ctx.close > ema) {
    ctx.mark("cross_up", { price: ctx.close, text: "↑", time: ctx.time });
  }
}

Not a study

No onEvent, no ctx.emit. For collectable setups use a definition.

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