BBANDS (Bollinger Bands)

Bollinger Bands consist of a middle SMA with upper and lower bands at a standard deviation distance. They expand during high volatility and contract during low volatility.

Declaration

function init(ctx) {
  ctx.indicator('bb', 'BBANDS', { period: 20, stdDev: 2 });
}

Options

Option	Type	Default	Description
`period`	`number`	20	SMA lookback period
`stdDev`	`number`	2	Standard deviation multiplier
`source`	`string`	`'close'`	Price source

Output

Returns an object with three series, accessed via underscore naming:

Property	Description
`upper`	Upper band (SMA + stdDev x sigma)
`middle`	Middle band (SMA)
`lower`	Lower band (SMA - stdDev x sigma)

Accessing Values

function onBar(ctx, i) {
  const upper = ctx.ind.bb_upper[i];
  const middle = ctx.ind.bb_middle[i];
  const lower = ctx.ind.bb_lower[i];
}

Use Cases

Bollinger Bounce (Mean Reversion)

function onBar(ctx, i) {
  const close = ctx.series.close[i];
  const lower = ctx.ind.bb_lower[i];
  const upper = ctx.ind.bb_upper[i];
  
  if (close <= lower) {
    ctx.order.market('ASSET', 1, { signal: 'buy', reason: 'bb_bounce_lower' });
  }
  if (close >= upper) {
    ctx.order.close('ASSET', { signal: 'sell', reason: 'bb_touch_upper' });
  }
}

Bollinger Squeeze (Breakout)

function onBar(ctx, i) {
  const bandwidth = (ctx.ind.bb_upper[i] - ctx.ind.bb_lower[i]) / ctx.ind.bb_middle[i];
  const prevBandwidth = (ctx.ind.bb_upper[i-1] - ctx.ind.bb_lower[i-1]) / ctx.ind.bb_middle[i-1];
  
  // Squeeze: narrow bands followed by expansion
  if (bandwidth > prevBandwidth * 1.5 && ctx.series.close[i] > ctx.ind.bb_upper[i]) {
    ctx.order.market('ASSET', 1, { signal: 'buy', reason: 'bb_squeeze_breakout' });
  }
}

Calculation

Middle = SMA(Close, period)
Upper = Middle + stdDev x StdDeviation(Close, period)
Lower = Middle - stdDev x StdDeviation(Close, period)

Keltner Channels - ATR-based bands (less sensitive)
ATR - Volatility measure
Donchian - High/low channel bands