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Spreadsheet Features

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Even for basic features like date storage, the official Excel formats store the same content in different ways. The parsers are expected to convert from the underlying file format representation to the Common Spreadsheet Format. Writers are expected to serialize SheetJS workbooks in the underlying file format.

The following topics are covered in sub-pages:

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Row and Column Properties

Format Support (click to show)

Row Properties: XLSX/M, XLSB, BIFF8 XLS, XLML, SYLK, DOM, ODS

Column Properties: XLSX/M, XLSB, BIFF8 XLS, XLML, SYLK, DOM

Row and Column properties are not extracted by default when reading from a file and are not persisted by default when writing to a file. The option cellStyles: true must be passed to the relevant read or write function.

Column Properties

The !cols array in each worksheet, if present, is a collection of ColInfo objects which have the following properties:

type ColInfo = {
  /* visibility */
  hidden?: boolean; // if true, the column is hidden

  /* column width is specified in one of the following ways: */
  wpx?:    number;  // width in screen pixels
  width?:  number;  // width in Excel "Max Digit Width", width*256 is integral
  wch?:    number;  // width in characters

  /* other fields for preserving features from files */
  level?:  number;  // 0-indexed outline / group level
  MDW?:    number;  // Excel "Max Digit Width" unit, always integral
};

Row Properties

The !rows array in each worksheet, if present, is a collection of RowInfo objects which have the following properties:

type RowInfo = {
  /* visibility */
  hidden?: boolean; // if true, the row is hidden

  /* row height is specified in one of the following ways: */
  hpx?:    number;  // height in screen pixels
  hpt?:    number;  // height in points

  level?:  number;  // 0-indexed outline / group level
};

Outline / Group Levels Convention

The Excel UI displays the base outline level as 1 and the max level as 8. Following JS conventions, SheetJS uses 0-indexed outline levels wherein the base outline level is 0 and the max level is 7.

Why are there three width types? (click to show)

There are three different width types corresponding to the three different ways spreadsheets store column widths:

SYLK and other plain text formats use raw character count. Contemporaneous tools like Visicalc and Multiplan were character based. Since the characters had the same width, it sufficed to store a count. This tradition was continued into the BIFF formats.

SpreadsheetML (2003) tried to align with HTML by standardizing on screen pixel count throughout the file. Column widths, row heights, and other measures use pixels. When the pixel and character counts do not align, Excel rounds values.

XLSX internally stores column widths in a nebulous "Max Digit Width" form. The Max Digit Width is the width of the largest digit when rendered (generally the "0" character is the widest). The internal width must be an integer multiple of the width divided by 256. ECMA-376 describes a formula for converting between pixels and the internal width. This represents a hybrid approach.

Read functions attempt to populate all three properties. Write functions will try to cycle specified values to the desired type. In order to avoid potential conflicts, manipulation should delete the other properties first. For example, when changing the pixel width, delete the wch and width properties.

Implementation details (click to show)

Row Heights

Excel internally stores row heights in points. The default resolution is 72 DPI or 96 PPI, so the pixel and point size should agree. For different resolutions they may not agree, so the library separates the concepts.

Even though all of the information is made available, writers are expected to follow the priority order:

use hpx pixel height if available
use hpt point height if available

Column Widths

Given the constraints, it is possible to determine the MDW without actually inspecting the font! The parsers guess the pixel width by converting from width to pixels and back, repeating for all possible MDW and selecting the value that minimizes the error. XLML actually stores the pixel width, so the guess works in the opposite direction.

Even though all of the information is made available, writers are expected to follow the priority order:

use width field if available
use wpx pixel width if available
use wch character count if available

Number Formats

The cell.w formatted text for each cell is produced from cell.v and cell.z format. If the format is not specified, the Excel General format is used. The format can either be specified as a string or as an index into the format table. Readers are expected to populate workbook.SSF with the number format table. Writers are expected to serialize the table.

The following example creates a custom format from scratch:

var wb = {
  SheetNames: ["Sheet1"],
  Sheets: {
    Sheet1: {
      "!ref":"A1:C1",
      A1: { t:"n", v:10000 },                    // <-- General format
      B1: { t:"n", v:10000, z: "0%" },           // <-- Builtin format
      C1: { t:"n", v:10000, z: "\"T\"\ #0.00" }  // <-- Custom format
    }
  }
}

The rules are slightly different from how Excel displays custom number formats. In particular, literal characters must be wrapped in double quotes or preceded by a backslash. For more info, see the Excel documentation article Create or delete a custom number format or ECMA-376 18.8.31 (Number Formats)

Default Number Formats (click to show)

The default formats are listed in ECMA-376 18.8.30:

ID	Format
0	`General`
1	`0`
2	`0.00`
3	`#,##0`
4	`#,##0.00`
9	`0%`
10	`0.00%`
11	`0.00E+00`
12	`# ?/?`
13	`# ??/??`
14	`m/d/yy` (see below)
15	`d-mmm-yy`
16	`d-mmm`
17	`mmm-yy`
18	`h:mm AM/PM`
19	`h:mm:ss AM/PM`
20	`h:mm`
21	`h:mm:ss`
22	`m/d/yy h:mm`
37	`#,##0 ;(#,##0)`
38	`#,##0 ;[Red](#,##0)`
39	`#,##0.00;(#,##0.00)`
40	`#,##0.00;[Red](#,##0.00)`
45	`mm:ss`
46	`[h]:mm:ss`
47	`mmss.0`
48	`##0.0E+0`
49	`@`

Format 14 (m/d/yy) is localized by Excel: even though the file specifies that number format, it will be drawn differently based on system settings. It makes sense when the producer and consumer of files are in the same locale, but that is not always the case over the Internet. To get around this ambiguity, parse functions accept the dateNF option to override the interpretation of that specific format string.

Cell Comments

Format Support (click to show)

Simple Notes/Comments: XLSX/M, XLSB, BIFF8 XLS (read only), XLML, ODS (read only)

Threaded Comments: XLSX/M, XLSB (read only)

Cell comments are objects stored in the c array of cell objects. The actual contents of the comment are split into blocks based on the comment author. The a field of each comment object is the author of the comment and the t field is the plain text representation.

For example, the following snippet appends a cell comment into cell A1:

if(!ws.A1.c) ws.A1.c = [];
ws.A1.c.push({a:"SheetJS", t:"I'm a little comment, short and stout!"});

Note: XLSB enforces a 54 character limit on the Author name. Names longer than 54 characters may cause issues with other formats.

To mark a comment as normally hidden, set the hidden property:

if(!ws.A1.c) ws.A1.c = [];
ws.A1.c.push({a:"SheetJS", t:"This comment is visible"});

if(!ws.A2.c) ws.A2.c = [];
ws.A2.c.hidden = true;
ws.A2.c.push({a:"SheetJS", t:"This comment will be hidden"});

Threaded Comments

Introduced in Excel 365, threaded comments are plain text comment snippets with author metadata and parent references. They are supported in XLSX and XLSB.

To mark a comment as threaded, each comment part must have a true T property:

if(!ws.A1.c) ws.A1.c = [];
ws.A1.c.push({a:"SheetJS", t:"This is not threaded"});

if(!ws.A2.c) ws.A2.c = [];
ws.A2.c.hidden = true;
ws.A2.c.push({a:"SheetJS", t:"This is threaded", T: true});
ws.A2.c.push({a:"JSSheet", t:"This is also threaded", T: true});

There is no Active Directory or Office 365 metadata associated with authors in a thread.

Sheet Visibility

Format Support (click to show)

Hidden Sheets: XLSX/M, XLSB, BIFF8/BIFF5 XLS, XLML

Very Hidden Sheets: XLSX/M, XLSB, BIFF8/BIFF5 XLS, XLML

Excel enables hiding sheets in the lower tab bar. The sheet data is stored in the file but the UI does not readily make it available. Standard hidden sheets are revealed in the "Unhide" menu. Excel also has "very hidden" sheets which cannot be revealed in the menu. It is only accessible in the VB Editor!

The visibility setting is stored in the Hidden property of sheet props array.

Value	Definition	VB Editor "Visible" Property
0	Visible	`-1 - xlSheetVisible`
1	Hidden	`0 - xlSheetHidden`
2	Very Hidden	`2 - xlSheetVeryHidden`

If the respective Sheet entry does not exist or if the Hidden property is not set, the worksheet is visible.

List all worksheets and their visibility settings

wb.Workbook.Sheets.map(function(x) { return [x.name, x.Hidden] })
// [ [ 'Visible', 0 ], [ 'Hidden', 1 ], [ 'VeryHidden', 2 ] ]

Check if worksheet is visible

Non-Excel formats do not support the Very Hidden state. The best way to test if a sheet is visible is to check if the Hidden property is logical truth:

wb.Workbook.Sheets.map(function(x) { return [x.name, !x.Hidden] })
// [ [ 'Visible', true ], [ 'Hidden', false ], [ 'VeryHidden', false ] ]

Live Example (click to show)

This test file has three sheets:

"Visible" is visible
"Hidden" is hidden
"VeryHidden" is very hidden

Live demo

function Visibility(props) {
  const [sheets, setSheets] = React.useState([]);
  const names = [ "Visible", "Hidden", "Very Hidden" ];

  React.useEffect(async() => {
    const f = await fetch("/files/sheet_visibility.xlsx");
    const ab = await f.arrayBuffer();
    const wb = XLSX.read(ab);

    /* State will be set to the `Sheets` property array */
    setSheets(wb.Workbook.Sheets);
  }, []);

  return (<table>
    <thead><tr><th>Name</th><th>Value</th><th>Hidden</th></tr></thead>
    <tbody>{sheets.map((x,i) => (<tr key={i}>

      <td>{x.name}</td>

      <td>{x.Hidden} - {names[x.Hidden]}</td>

      <td>{!x.Hidden ? "No" : "Yes"}</td>

    </tr>))}</tbody></table>);
}

VBA and Macros

Format Support (click to show)

VBA Modules: XLSM, XLSB, BIFF8 XLS

VBA Macros are stored in a special data blob that is exposed in the vbaraw property of the workbook object when the bookVBA option is true. They are supported in XLSM, XLSB, and BIFF8 XLS formats. The supported format writers automatically insert the data blobs if it is present in the workbook and associate with the worksheet names.

The vbaraw property stores raw bytes. SheetJS Pro offers a special component for extracting macro text from the VBA blob, editing the VBA project, and exporting new VBA blobs.

Round-tripping Macro Enabled Files

In order to preserve macro when reading and writing files, the bookVBA option must be set to true when reading and when writing. In addition, the output file format must support macros. XLSX notably does not support macros, and XLSM should be used in its place:

/* Reading data */
var wb = XLSX.read(data, { bookVBA: true }); // read file and distill VBA blob
var vbablob = wb.vbaraw;

Code Names

By default, Excel will use ThisWorkbook or a translation DieseArbeitsmappe for the workbook. Each worksheet will be identified using the default Sheet# naming pattern even if the worksheet names have changed.

A custom workbook code name will be stored in wb.Workbook.WBProps.CodeName. For exports, assigning the property will override the default value.

Worksheet and Chartsheet code names are in the worksheet properties object at wb.Workbook.Sheets[i].CodeName. Macrosheets and Dialogsheets are ignored.

The readers and writers preserve the code names, but they have to be manually set when adding a VBA blob to a different workbook.

Macrosheets

Older versions of Excel also supported a non-VBA "macrosheet" sheet type that stored automation commands. These are exposed in objects with the !type property set to "macro".

Under the hood, Excel treats Macrosheets as normal worksheets with special interpretation of the function expressions.

Detecting Macros in Workbooks

The vbaraw field will only be set if macros are present. Macrosheets will be explicitly flagged. Combining the two checks yields a simple function:

function wb_has_macro(wb/*:workbook*/)/*:boolean*/ {
  if(!!wb.vbaraw) return true;
  const sheets = wb.SheetNames.map((n) => wb.Sheets[n]);
  return sheets.some((ws) => !!ws && ws['!type']=='macro');
}

14 KiB Raw Blame History

Spreadsheet Features

Row and Column Properties

Number Formats

Cell Comments

Sheet Visibility

VBA and Macros

Round-tripping Macro Enabled Files

Code Names

Macrosheets

Detecting Macros in Workbooks

14 KiB

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