sheetjs/docbits/52_datatype.md

#### Data Types

The raw value is stored in the `v` value property, interpreted based on the `t`
type property.  This separation allows for representation of numbers as well as
numeric text.  There are 6 valid cell types:

| Type | Description                                                           |
| :--: | :-------------------------------------------------------------------- |
| `b`  | Boolean: value interpreted as JS `boolean`                            |
| `e`  | Error: value is a numeric code and `w` property stores common name ** |
| `n`  | Number: value is a JS `number` **                                     |
| `d`  | Date: value is a JS `Date` object or string to be parsed as Date **   |
| `s`  | Text: value interpreted as JS `string` and written as text **         |
| `z`  | Stub: blank stub cell that is ignored by data processing utilities ** |

<details>
  <summary><b>Error values and interpretation</b> (click to show)</summary>

|  Value | Error Meaning   |
| -----: | :-------------- |
| `0x00` | `#NULL!`        |
| `0x07` | `#DIV/0!`       |
| `0x0F` | `#VALUE!`       |
| `0x17` | `#REF!`         |
| `0x1D` | `#NAME?`        |
| `0x24` | `#NUM!`         |
| `0x2A` | `#N/A`          |
| `0x2B` | `#GETTING_DATA` |

</details>

Type `n` is the Number type. This includes all forms of data that Excel stores
as numbers, such as dates/times and Boolean fields.  Excel exclusively uses data
that can be fit in an IEEE754 floating point number, just like JS Number, so the
`v` field holds the raw number.  The `w` field holds formatted text.  Dates are
stored as numbers by default and converted with `XLSX.SSF.parse_date_code`.

Type `d` is the Date type, generated only when the option `cellDates` is passed.
Since JSON does not have a natural Date type, parsers are generally expected to
store ISO 8601 Date strings like you would get from `date.toISOString()`.  On
the other hand, writers and exporters should be able to handle date strings and
JS Date objects.  Note that Excel disregards timezone modifiers and treats all
dates in the local timezone.  The library does not correct for this error.

Type `s` is the String type.  Values are explicitly stored as text.  Excel will
interpret these cells as "number stored as text".  Generated Excel files
automatically suppress that class of error, but other formats may elicit errors.

Type `z` represents blank stub cells.  They are generated in cases where cells
have no assigned value but hold comments or other metadata. They are ignored by
the core library data processing utility functions.  By default these cells are
not generated; the parser `sheetStubs` option must be set to `true`.


#### Dates

<details>
  <summary><b>Excel Date Code details</b> (click to show)</summary>

By default, Excel stores dates as numbers with a format code that specifies date
processing.  For example, the date `19-Feb-17` is stored as the number `42785`
with a number format of `d-mmm-yy`.  The `SSF` module understands number formats
and performs the appropriate conversion.

XLSX also supports a special date type `d` where the data is an ISO 8601 date
string.  The formatter converts the date back to a number.

The default behavior for all parsers is to generate number cells.  Setting
`cellDates` to true will force the generators to store dates.

</details>

<details>
  <summary><b>Time Zones and Dates</b> (click to show)</summary>

Excel has no native concept of universal time.  All times are specified in the
local time zone.  Excel limitations prevent specifying true absolute dates.

Following Excel, this library treats all dates as relative to local time zone.

</details>

<details>
  <summary><b>Epochs: 1900 and 1904</b> (click to show)</summary>

Excel supports two epochs (January 1 1900 and January 1 1904), see
["1900 vs. 1904 Date System" article](http://support2.microsoft.com/kb/180162).
The workbook's epoch can be determined by examining the workbook's
`wb.Workbook.WBProps.date1904` property:

```js
!!(((wb.Workbook||{}).WBProps||{}).date1904)
```

</details>