Intervals

The interval option controls the time gap between bars. Two flavours:

• Fixed — every step is the same number of milliseconds.
• Calendar-aware — months and years respect the calendar (real lengths, day-of-month preserved).

Shorthand strings

String	Meaning	Calendar-aware?
"1m"	1 minute	no
"5m"	5 minutes	no
"1h"	1 hour	no
"1d"	1 day	no
"1w"	1 week	no
"1mo"	1 calendar month	yes
"3mo"	3 calendar months	yes
"1y"	1 calendar year	yes

The number can be any positive integer: "15m", "2h", "6mo", "5y", etc. Zero ("0d") is rejected.

js generateStock({ bars: 100, interval: '15m', startDate: '2024-01-01T09:30:00Z' }); generateStock({ bars: 30, interval: '1mo', startDate: '1999-08-01' }); generateStock({ bars: 25, interval: '1y', startDate: '2000-01-01' });

Raw milliseconds

Pass any positive number to use that many ms per bar:

js const ms2h = 2 * 60 * 60 * 1000; generateStock({ bars: 100, interval: ms2h });

This is fixed (no calendar awareness), useful for unusual intervals like 4 hours or 30 minutes.

Calendar awareness

"1mo" and "1y" are calendar-aware. They step to the same day of the next month or year:

js generateStock({ bars: 6, interval: '1mo', startDate: '1999-08-01' }); // Bar timestamps: 1999-08-01, 1999-09-01, 1999-10-01, 1999-11-01, 1999-12-01, 2000-01-01

js generateStock({ bars: 5, interval: '1y', startDate: '1999-08-01' }); // Bar timestamps: 1999-08-01, 2000-08-01, 2001-08-01, 2002-08-01, 2003-08-01

Leap years are handled. January 31 + 1mo rolls over the way JavaScript's Date.setUTCMonth does (lands in early March).

Why this matters

Without calendar awareness, "1 month" would mean 30 days, so a chart anchored to "1st of the month" would slowly drift over time. Calendar-aware stepping keeps the day-of-month aligned for the life of the chart.

Where the interval shows up

The generated Stock carries an interval field expressed in milliseconds:

js const stock = generateStock({ interval: '1mo', bars: 12 }); stock.interval; // 2592000000 (30-day approximation)

For calendar-aware units this is an approximate number — useful for downstream consumers that just need a single representative duration. The actual bar timestamps are computed exactly via the calendar logic, not by repeatedly adding interval.

Mixed intervals across a market

Each stock in a market can have its own interval. This is how you'd build, say, an FX dashboard mixing daily and intraday symbols:

js generateMarket({ seed: 'mixed', stocks: [ { symbol: 'EURUSD', interval: '1h', bars: 720 }, // 30 days of hourly { symbol: 'SPX', interval: '1d', bars: 365 } // 1 year of daily ] });

When you put both on a multi-line chart, the union of their timelines becomes the X axis automatically.

Helpers

If you want to step time the same way the generator does, the helpers are exported:

```js import { parseInterval, parseIntervalSpec } from 'stock-market-gen';

parseInterval('1d'); // 86400000 parseInterval('1mo'); // 2592000000 (approximate)

parseIntervalSpec('1mo'); // { unit: 'mo', n: 1, calendar: true, ms: 2592000000 } ```

parseIntervalSpec is the structured version — useful if you need to know whether the interval is calendar-aware before stepping.