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# Custom Selections

:::info Draft

This documentation is still a work in progress. If you have any questions, ask to the [discussions](https://github.com/gpbl/react-day-picker/discussions) page on Github.

:::

If the built-in [selection modes](../docs/selection-modes.mdx) does not satisfy for your app’s requirements, you can control the selection behavior using the [`onDayClick`](../api/interfaces/PropsBase.md#ondayclick) and [`modifiers`](../api/interfaces/PropsBase.md#modifiers) props:

| Prop         | Type                                                        | Description                               |
| ------------ | ----------------------------------------------------------- | ----------------------------------------- |
| `onDayClick` | [`DayEventHandler`](../api/type-aliases/DayEventHandler.md) | Callback when a day is clicked.           |
| `modifiers`  | [`Modifiers`](../api/type-aliases/Modifiers.md)             | An object with the modifiers of the days. |

This prop is a function that receives the clicked day and the modifiers of the day as arguments.

## Examples

### Week Selection

The following example shows how to select the whole week when a day is clicked.

Note the use of the `startOfWeek` and `endOfWeek` functions from [date-fns](https://date-fns.org) and how the `selectedWeek` state is passed to the `modifiers` prop.

```tsx
import React, { useState } from "react";

import { endOfWeek, startOfWeek } from "date-fns";
import { DateRange, DayPicker, isDateInRange } from "react-day-picker";

/** Select the whole week when the day is clicked. */
export function CustomWeek() {
  const [selectedWeek, setSelectedWeek] = useState<DateRange | undefined>();

  return (
    <DayPicker
      showWeekNumber
      showOutsideDays
      modifiers={{
        selected: selectedWeek,
        range_start: selectedWeek?.from,
        range_end: selectedWeek?.to,
        range_middle: (date: Date) =>
          selectedWeek
            ? isDateInRange(date, selectedWeek, { excludeEnds: true })
            : false
      }}
      onDayClick={(day, modifiers) => {
        if (modifiers.selected) {
          setSelectedWeek(undefined); // clear the selection if the day is already selected
          return;
        }
        setSelectedWeek({
          from: startOfWeek(day),
          to: endOfWeek(day)
        });
      }}
      footer={
        selectedWeek &&
        `Week from ${selectedWeek?.from?.toLocaleDateString()} to
            ${selectedWeek?.to?.toLocaleDateString()}`
      }
    />
  );
}
```

<BrowserWindow>
  <Examples.CustomWeek />
</BrowserWindow>

### Single Selection

For example, to implement the "single selection" behavior (like when `mode="single"`):

```tsx
import { useState } from "react";

import { DayPicker, DayPickerProps } from "react-day-picker";

export function CustomSingle() {
  const [selectedDate, setSelectedDate] = useState<Date | undefined>();

  const modifiers: DayPickerProps["modifiers"] = {};
  if (selectedDate) {
    modifiers.selected = selectedDate;
  }
  return (
    <DayPicker
      modifiers={modifiers}
      onDayClick={(day, modifiers) => {
        if (modifiers.selected) {
          setSelectedDate(undefined);
        } else {
          setSelectedDate(day);
        }
      }}
      footer={selectedDate && `You selected ${selectedDate.toDateString()}`}
    />
  );
}
```

<BrowserWindow>
  <Examples.CustomSingle />
</BrowserWindow>

### Multi Selections

The case of a multi-days select is a bit more complex as it deals with an array. The following example replicates the `mode="multiple"`
selection mode.

```tsx
import { useState } from "react";

import { isSameDay } from "date-fns";
import { DayMouseEventHandler, DayPicker } from "react-day-picker";

export function CustomMultiple() {
  const [value, setValue] = useState<Date[]>([]);

  const handleDayClick: DayMouseEventHandler = (day, modifiers) => {
    const newValue = [...value];
    if (modifiers.selected) {
      const index = value.findIndex((d) => isSameDay(day, d));
      newValue.splice(index, 1);
    } else {
      newValue.push(day);
    }
    setValue(newValue);
  };

  const handleResetClick = () => setValue([]);

  let footer = <>Please pick one or more days.</>;

  if (value.length > 0)
    footer = (
      <>
        You selected {value.length} days.{" "}
        <button onClick={handleResetClick}>Reset</button>
      </>
    );

  return (
    <DayPicker
      onDayClick={handleDayClick}
      modifiers={{ selected: value }}
      footer={footer}
    />
  );
}
```

<BrowserWindow>
  <Examples.CustomMultiple />
</BrowserWindow>