# weekStart

Calendar heatmap: the first day of the week (the top row) — `monday` or `sunday`.

Canonical: https://chart.syidax.com/docs/options/weekStart/

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## Definition

| Item | Value |
| --- | --- |
| JavaScript property | `weekStart` |
| HTML attribute | `week-start` |
| Type | `CalendarWeekStart` |
| Default | `undefined` |
| Allowed values | `monday`, `sunday` |

undefined means this property was not explicitly set. The effective value may depend on the chart type and other settings.

- [CalendarWeekStart](https://chart.syidax.com/docs/types/CalendarWeekStart.md) — Type definition

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## Configuration example

```javascript
// Register sy-calendar-heatmap and create the element before configuring it.
chart.weekStart = "monday";
```

- [Calendar Heatmap · Complete examples and API](https://chart.syidax.com/docs/components/calendar-heatmap.md)

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## Related documentation

A property with the same name may have different types and defaults across charts. When using a direct tag, follow that chart's documentation below.

- [Shared facade and direct tags](https://chart.syidax.com/docs/concepts.md)
- [sy-calendar-heatmap](https://chart.syidax.com/docs/components/calendar-heatmap.md#property-weekStart)