docs.sheetjs.com/docz/docs/08-api/03-parse-options.md

sidebar_position	hide_table_of_contents	title
3	true	Reading Files

XLSX.read(data, options)

read attempts to parse data and return a workbook object

The type of the options object determines how data is interpreted. For string data, the default interpretation is Base64.

XLSX.readFile(filename, options)

readFile attempts to read a local file with specified filename.

:::caution pass

This method only works in specific environments. It does not work in browsers!

The NodeJS installation note includes additional instructions for non-standard use cases.

:::

Parsing Options

The read functions accept an options argument:

Option Name	Default	Description
type		Input data encoding (see Input Type below)
raw	false	If true, plain text parsing will not parse values **
dense	false	If true, use a dense worksheet representation **
codepage		If specified, use code page when appropriate **
cellFormula	true	Save formulae to the .f field
cellHTML	true	Parse rich text and save HTML to the .h field
cellNF	false	Save number format string to the .z field
cellStyles	false	Save style/theme info to the .s field
cellText	true	Generated formatted text to the .w field
cellDates	false	Store dates as type d (default is n)
dateNF		If specified, use the string for date code 14 **
sheetStubs	false	Create cell objects of type z for stub cells
sheetRows	0	If >0, read the first sheetRows rows **
bookDeps	false	If true, parse calculation chains
bookFiles	false	If true, add raw files to book object **
bookProps	false	If true, only parse enough to get book metadata **
bookSheets	false	If true, only parse enough to get the sheet names
bookVBA	false	If true, copy VBA blob to vbaraw field **
password	""	If defined and file is encrypted, use password **
WTF	false	If true, throw errors on unexpected file features **
sheets		If specified, only parse specified sheets **
PRN	false	If true, allow parsing of PRN files **
xlfn	false	If true, preserve _xlfn. prefixes in formulae **
FS		DSV Field Separator override
UTC	true	If explicitly false, parse text dates in local time

• Even if cellNF is false, formatted text will be generated and saved to .w
• In some cases, sheets may be parsed even if bookSheets is false.
• Excel aggressively tries to interpret values from CSV and other plain text. This leads to surprising behavior! The raw option suppresses value parsing.
• bookSheets and bookProps combine to give both sets of information
• Deps will be an empty object if bookDeps is false
• bookFiles behavior depends on file type:
  • keys array (paths in the ZIP) for ZIP-based formats
  • files hash (mapping paths to objects representing the files) for ZIP
  • cfb object for formats using CFB containers
• 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)
• By default all worksheets are parsed. sheets restricts based on input type:
  • number: zero-based index of worksheet to parse (0 is first worksheet)
  • string: name of worksheet to parse (case insensitive)
  • array of numbers and strings to select multiple worksheets.
• 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.
• codepage is applied to BIFF2 - BIFF5 files without CodePage records and to CSV files without BOM in type:"binary". BIFF8 XLS always defaults to 1200.
• PRN affects parsing of text files without a common delimiter character.
• Currently only XOR encryption is supported. Unsupported error will be thrown for files employing other encryption methods.
• Newer Excel functions are serialized with the _xlfn. prefix, hidden from the user. SheetJS will strip _xlfn. normally. The xlfn option preserves them.
• WTF is mainly for development. By default, the parser will suppress read errors on single worksheets, allowing you to read from the worksheets that do parse properly. Setting WTF:true forces those errors to be thrown.
• By default, "sparse" mode worksheets are generated. Individual cells are accessed by indexing the worksheet object with an A1-Style address. "dense" worksheets store cells in an array of arrays at sheet["!data"].
• UTC applies to CSV, Text and HTML formats. When explicitly set to false, the parsers will assume the files are specified in local time. By default, as is the case for other file formats, dates and times are interpreted in UTC.

Input Type

Strings can be interpreted in multiple ways. The type parameter for read tells the library how to parse the data argument:

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 text files valid? (click to hide)

Excel is extremely aggressive in reading files. Adding an XLS extension to any display text file (where the only characters are ANSI display chars) tricks Excel into thinking that the file is potentially a CSV or TSV file, even if it is only one column! This library attempts to replicate that behavior.

The best approach is to validate the desired worksheet and ensure it has the expected number of rows or columns. Extracting the range is extremely simple:

var range = XLSX.utils.decode_range(worksheet['!ref']);
var ncols = range.e.c - range.s.c + 1, nrows = range.e.r - range.s.r + 1;