> ## Documentation Index
> Fetch the complete documentation index at: https://docs.darvas.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Support and resistance

> Auto-detect S/R levels via ta.pivothigh/pivotlow and draw them as forward-projecting arrow.right Line entities.

## What this builds

* Automatic swing high and swing low detection
* Each pivot gets a `Line` entity with `style: "arrow.right"` that projects forward
* Price label on each line

## Full script

```js theme={null}
// overlay = true
const leftBars  = input.int("Left bars",  5, { min: 1, max: 50 });
const rightBars = input.int("Right bars", 5, { min: 1, max: 50 });
const lineLen   = input.int("Line length (bars)", 50, { min: 5 });
const maxLines  = input.int("Max lines", 20, { min: 1, max: 50 });

const resistColor = input.color("Resistance color", "#ef4444CC");
const supportColor = input.color("Support color",   "#22c55eCC");

onBar(() => {
  const ph = ta.pivothigh(ctx.high, leftBars, rightBars);
  const pl = ta.pivotlow(ctx.low,   leftBars, rightBars);

  const pivotBar = ctx.i() - rightBars;

  if (!na(ph)) {
    Line(`sr_high_${pivotBar}`, {
      x1: pivotBar,
      y1: ph,
      x2: pivotBar + lineLen,
      y2: ph,
      color: resistColor,
      width: 1,
      style: "arrow.right",
      label: str.format("{}", math.round(ph, 1)),
    });
  }

  if (!na(pl)) {
    Line(`sr_low_${pivotBar}`, {
      x1: pivotBar,
      y1: pl,
      x2: pivotBar + lineLen,
      y2: pl,
      color: supportColor,
      width: 1,
      style: "arrow.right",
      label: str.format("{}", math.round(pl, 1)),
    });
  }
});
```

## Dynamic keys

Each pivot gets its own unique key (`sr_high_${pivotBar}`) so old lines persist on the chart while new ones are added. This means the chart can accumulate many lines over time - use `maxLines` logic (not shown above) or a fixed-size key pool if you want to cap line count.

## Capping old lines

To limit lines to the most recent `maxLines` pivots, maintain a counter and delete old ones:

```js theme={null}
let highCount = 0;

onBar(() => {
  const ph = ta.pivothigh(ctx.high, 5, 5);
  if (!na(ph)) {
    const pivotBar = ctx.i() - 5;
    const key = `ph_${pivotBar}`;

    Line(key, {
      x1: pivotBar, y1: ph,
      x2: pivotBar + 50, y2: ph,
      color: "#ef4444CC",
      style: "arrow.right",
    });

    highCount++;

    // Delete the line from 50 pivots ago
    const oldBar = pivotBar - 50 * 5; // approximate
    Line(`ph_${oldBar}`, { x1: 0, y1: 0, x2: 0, y2: 0, color: "#00000000" });
  }
});
```

## Related pages

<CardGroup cols={2}>
  <Card title="Pivots" href="/ta/pivots">
    ta.pivothigh/pivotlow - the lag explained.
  </Card>

  <Card title="Line entity" href="/entities/line">
    Full Line options including arrow\.right style.
  </Card>

  <Card title="str.*" href="/essentials/str">
    str.format for price labels.
  </Card>
</CardGroup>