Reading Files
The main SheetJS method for reading files is read. It expects developers to
supply the actual data in a supported representation.
The readFile helper method accepts a filename and tries to read the specified
file using standard APIs. It does not work in web browsers!
Parse file data and generate a SheetJS workbook object
var wb = XLSX.read(data, opts);
read attempts to parse data and return a workbook object
The type property of the opts object controls how data is
interpreted. For string data, the default interpretation is Base64.
Read a specified file and generate a SheetJS workbook object
var wb = XLSX.readFile(filename, opts);
readFile attempts to read a local file with specified filename.
readFile works in specific platforms. It does not support web browsers!
The NodeJS installation note includes additional instructions for non-standard use cases.
The SheetJS file format import codecs focus on raw data. Not all codecs support all features. Features not described in the documentation may not be extracted.
SheetJS Pro offers support for additional features, including styling, images, graphs, and PivotTables.
Parsing Options
The read functions accept an options argument:
Cell-Level Options
Dates
By default, for consistency with spreadsheet applications, date cells are stored
as numeric cells (type n) with special number formats. If cellDates is
enabled, date codes are converted to proper Date objects.
Excel file formats (including XLSX, XLSB, and XLS) support a locale-specific
date format, typically stored as date code 14 or the string m/d/yy. The
formatted text for some cells will change based on the computer locale. SheetJS
parsers use the en-US form by default. If the dateNF option is set, that
number format string will be used.
"Dates and Times" covers features in more detail.
Formulae
For some file formats, the cellFormula option must be explicitly enabled to
ensure that formulae are extracted.
Newer Excel functions are serialized with the _xlfn. prefix, hidden from the
user. By default, the file parsers will strip _xlfn. and similar prefixes.
If the xlfn option is enabled, the prefixes will be preserved.
The "Formulae" docs covers this in more detail.
Formatted Text
Many common spreadsheet formats (including XLSX, XLSB, and XLS) store numeric values and number formats. Applications are expected to use the number formats to display currency strings, dates, and other values.
Under the hood, parsers use the SSF Number Formatter library to generated formatted text.
By default, formatted text is generated. If the cellText option is false,
formatted text will not be written.
By default, cell number formats are not preserved. If the cellNF option is
enabled, number format strings will be saved to the z field of cell objects.
"Number Formats" covers the features in more detail.
Even if cellNF is false, formatted text will be generated and saved to w.
Text and Cell Styling
By default, SheetJS CE parsers focus on data extraction.
If the cellStyles option is true, other styling metadata including
row and column
properties will be parsed.
SheetJS Pro offers cell / text styling, conditional formatting and additional styling options.
HTML Formatted Text
Spreadsheet applications support a limited form of rich text styling.
If the cellHTML option is true, some file parsers will attempt to translate
the rich text to standard HTML with inner tags for bold text and other styles.
SheetJS Pro offers additional styling options, conversions for all supported file formats, and whole-worsheet HTML generation.
Sheet-Level Options
Dense
By default, the read and readFile functions generate "sparse" worksheets.
When the dense option is set to true, the functions will generate "dense"
worksheets that may be more efficient in modern browsers.
The "Cell Storage" section explains worksheet structures in more detail.
Utility functions that process SheetJS workbook objects typically support sparse and dense worksheets.
Range
Some file formats, including XLSX and XLS, can self-report worksheet ranges.
read and readFile assume the self-reported worksheet ranges are correct. If
files include cells outside this range, the parsers will save cell information
but other utility functions will ignore those cells.
If the sheetRows option is set, up to sheetRows rows will be parsed from the
worksheets. sheetRows-1 rows will be generated when looking at the JSON object
output (since the header row is counted as a row when parsing the data). The
!ref property of the worksheet will hold the adjusted range. For formats that
self-report sheet ranges, the !fullref property will hold the original range.
The nodim option instructs the parser to ignore self-reported ranges and use
the actual cells in the worksheet to determine the range. This addresses known
issues with non-compliant third-party exporters.
Stubs
Some file formats, including XLSX and XLS, can specify cells without cell data. For example, cells covered by a merged cell block are technically invalid but files may include metadata.
By default, the cells are skipped. If the sheetStubs option is true, these
cells will be parsed as stub cells
Book-Level Options
VBA
When a macro-enabled file is parsed, if the bookVBA option is true, the raw
VBA blob will be stored in the vbaraw property of the workbook.
"VBA and Macros" covers the features in more detail.
Implementation Details (click to show)
The bookVBA merely exposes the raw VBA CFB object. It does not parse the data.
XLSM and XLSB store the VBA CFB object in xl/vbaProject.bin. BIFF8 XLS mixes
the VBA entries alongside the core Workbook entry, so the library generates a
new blob from the XLS CFB container that works in XLSM and XLSB files.
Workbook Metadata
By default, the data from each worksheet is parsed.
If any of the following options are passed, parsers will not parse sheet data. They will parse enough of the workbook to extract the requested information.
| Option | Extracted Data |
|---|---|
bookProps | Workbook properties |
bookSheets | Worksheet names |
The options apply to XLSX, XLSB, XLS and XLML parsers.
Worksheets
By default, all worksheets are parsed. The sheets option limits which sheets
are parsed.
If the sheets option is a number, the number is interpreted as a zero-based
index. For example, sheets: 2 instructs the parser to read the third sheet.
If the sheets option is text, the string is interpreted as a worksheet name.
The name is case-insensitive. sheets: "Sheet1" instructs the parser to read
the worksheet named "Sheet1".
If the sheets option is an array of numbers and text, each worksheets will
be parsed. sheets: [2, "Sheet1"] instructs the parser to read the third sheet
and the sheet named "Sheet1". If the third worksheet is coincidentally named
"Sheet1", only one worksheet will be parsed
File-Level Options
Password Protection
SheetJS CE currently supports XOR encryption in XLS files. Errors will be thrown when trying to parse files using unsupported encryption methods.
SheetJS Pro offers support for additional encryption schemes, including the AES-CBC schemes used in XLSX / XLSM / XLSB files and the RC4 schemes used in newer XLS files.
Lotus Formatted Text (PRN)
Lotus Formatted Text (PRN) worksheets are plain text files that do not include
delimiter characters. Each cell in a column has the same width.
If the PRN option is set, the plaintext parser will attempt to parse some
plaintext files as if they follow the PRN format.
If the PRN option is set, text files that do not include commas or semicolons
or other common delimiters may not be parsed as expected.
This option should not be enabled unless it is known that the file was exported
from Lotus 1-2-3 or from Excel using the "Lotus Formatted Text (PRN)" format.
Value Parsing
Spreadsheet software including Excel aggressively try to interpret values from CSV and other plain text. This leads to surprising behavior1!
If the raw option is true, value parsing will be suppressed. All cells values
are treated as strings.
The raw option affects the following formats: HTML, CSV, PRN, DIF, RTF.
The raw option does not affect XLSX, XLSB, XLS and other file formats that
support explicit value typing.
See Issue #3331 in the SheetJS CE bug tracker for more details.
Code Page Encoding
Spreadsheet applications support a number of legacy encodings. Plaintext files will appear different when opened in different computers in different regions.
By default, the parsers use the most common "English (United States)" encodings.
The codepage option controls the encoding in BIFF2 - BIFF5 XLS files without
CodePage records, some legacy formats including DBF, and in CSV files without
BOM in type: "binary". BIFF8 XLS always defaults to 1200.
The codepage support library is not guaranteed to be loaded by default. The
"Installation" section describes how to
install and load the support library.
See "Legacy Codepages" for more details.
Date Processing
Plaintext formats may include date and time values without timezone info. The
time 12:30 AM is ambiguous.
In the wild, there are two popular approaches:
A) Spreadsheet software typically interpret time values using local timezones.
When opening a file in New York, 12:30 AM will be parsed as 12:30 AM ET.
When opening a file in Los Angeles, the time will be parsed as 12:30 AM PT.
B) APIs use UTC, the
most popular global time standard. 12:30 AM will be parsed as the absolute
moment in time corresponding to 8:30 PM EDT or 7:30 PM EST.
By default, the parsers assume files are specified in UTC. When the UTC option
is explicitly set to false, dates and times are interpreted in timezone of the
web browser or JavaScript engine.
Delimiter-Separated Values
The plaintext parser applies a number of heuristics to determine if files are
CSV (fields separated by commas), TSV (fields separated by tabs), PSV (fields
separated by |) or SSV (fields separated by ;). The heuristics are based on
the presence of characters not in a double-quoted value.
The FS option instructs the parser to use the specified delimiter if multiple
delimiter characters are in the text. This bypasses the default heuristics.
Internal Files
Some file formats are structured as larger containers that include sub-files. For example, XLSX files are ZIP files with XML sub-files.
If the bookFiles option is true, each sub-file will be preserved in the
workbook. The behavior depends on file type:
keysarray (paths in the ZIP) for ZIP-based formatsfileshash (mapping paths to objects representing the files) for ZIPcfbobject for formats using CFB containers
Parsing Errors
By default, the workbook parser will suppress errors when parsing worksheets. This ensures the valid worksheets from a multi-sheet workbook are parsed.
If the WTF option is enabled, the errors will not be suppressed.
Input Type
The type parameter for read controls how data is interpreted:
type | expected input |
|---|---|
base64 | string: Base64 encoding of the file |
binary | string: binary string (byte n is data.charCodeAt(n)) |
string | string: JS string (only appropriate for UTF-8 text formats) |
buffer | nodejs Buffer |
array | array: array of 8-bit unsigned integers (byte n is data[n]) |
file | string: path of file that will be read (nodejs only) |
Some common types are automatically deduced from the data input type, including
NodeJS Buffer objects, Uint8Array and ArrayBuffer objects, and arrays of
numbers.
When a JS string is passed with no type, the library assumes the data is a
Base64 string. FileReader#readAsBinaryString or ASCII data requires "binary"
type. DOM strings including FileReader#readAsText should use type "string".
Guessing File Type
Implementation Details (click to show)
Excel and other spreadsheet tools read the first few bytes and apply other
heuristics to determine a file type. This enables file type punning: renaming
files with the .xls extension will tell your computer to use Excel to open the
file but Excel will know how to handle it. This library applies similar logic:
| Byte 0 | Raw File Type | Spreadsheet Types |
|---|---|---|
0xD0 | CFB Container | BIFF 5/8 or protected XLSX/XLSB or WQ3/QPW or XLR |
0x09 | BIFF Stream | BIFF 2/3/4/5 |
0x3C | XML/HTML | SpreadsheetML / Flat ODS / UOS1 / HTML / plain text |
0x50 | ZIP Archive | XLSB or XLSX/M or ODS or UOS2 or NUMBERS or text |
0x49 | Plain Text | SYLK or plain text |
0x54 | Plain Text | DIF or plain text |
0xEF | UTF-8 Text | SpreadsheetML / Flat ODS / UOS1 / HTML / plain text |
0xFF | UTF-16 Text | SpreadsheetML / Flat ODS / UOS1 / HTML / plain text |
0x00 | Record Stream | Lotus WK* or Quattro Pro or plain text |
0x7B | Plain text | RTF or plain text |
0x0A | Plain text | SpreadsheetML / Flat ODS / UOS1 / HTML / plain text |
0x0D | Plain text | SpreadsheetML / Flat ODS / UOS1 / HTML / plain text |
0x20 | Plain text | SpreadsheetML / Flat ODS / UOS1 / HTML / plain text |
DBF files are detected based on the first byte as well as the third and fourth bytes (corresponding to month and day of the file date)
Works for Windows files are detected based on the BOF record with type 0xFF
Plain text format guessing follows the priority order:
| Format | Test |
|---|---|
| XML | <?xml appears in the first 1024 characters |
| HTML | starts with < and HTML tags appear in the first 1024 characters |
| XML | starts with < and the first tag is valid |
| RTF | starts with {\rt |
| DSV | starts with sep= followed by field delimiter and line separator |
| DSV | more unquoted | chars than ; \t or , in the first 1024 |
| DSV | more unquoted ; chars than \t or , in the first 1024 |
| TSV | more unquoted \t chars than , chars in the first 1024 |
| CSV | one of the first 1024 characters is a comma "," |
| ETH | starts with socialcalc:version: |
| PRN | PRN option is set to true |
| CSV | (fallback) |
HTML tags include html, table, head, meta, script, style, div
Why are random files valid? (click to hide)
Excel is extremely aggressive in reading files. Adding the XLS extension to any file tricks Excel into processing the file.
If the file matches certain heuristics, Excel will use a format-specific parser.
If it cannot deduce the file type, Excel will parse the unknown file as if it were CSV or TSV. SheetJS attempts to replicate that behavior.