Bar context

onBar(() => {
  const close  = ctx.close();    // current bar close
  const prev   = ctx.close(1);   // previous bar close
  const change = close - prev;
});

// Correct: pass ctx.close as a function reference
const rsi = ta.rsi(ctx.close, 14);

// Correct: input.source returns the same shape
const src = input.source("Source", "close");
const rsi2 = ta.rsi(src, 14);

// Wrong: calling ctx.close() gives you a scalar, not a source
// const rsi3 = ta.rsi(ctx.close(), 14); // TypeError

onBar(() => {
  const c0 = ctx.close();   // current close
  const c3 = ctx.close(3);  // close 3 bars ago

  // Detect 3-bar momentum
  const momentum = c0 - c3;
  plot("3-bar Momentum", momentum);

  // Log bar info on last bar
  if (ctx.isLast()) {
    console.log(ctx.instId, ctx.bar, "index:", ctx.i());
  }
});