catamphetamine / Read Excel File
Programming Languages
read-excel-file
Read small to medium *.xlsx
files in a browser or Node.js. Parse to JSON with a strict schema.
Restrictions
There have been some complaints about this library not being able to handle large *.xlsx
spreadsheets. It's true that this library's main point have been usability and convenience, and not performance or the ability to handle huge datasets. For example, the time of parsing a 2000 rows / 20 columns file is about 3 seconds, and when parsing a 30k+ rows file, it may throw a RangeError: Maximum call stack size exceeded
. So, for handling huge datasets, use something like xlsx
package instead. This library is suitable for handling small to medium *.xlsx
files.
GitHub
On March 9th, 2020, GitHub, Inc. silently banned my account (and all my libraries) without any notice. I opened a support ticked but they didn't answer. Because of that, I had to move all my libraries to GitLab.
Install
npm install read-excel-file --save
If you're not using a bundler then use a standalone version from a CDN.
Browser
<input type="file" id="input" />
import readXlsxFile from 'read-excel-file'
const input = document.getElementById('input')
input.addEventListener('change', () => {
readXlsxFile(input.files[0]).then((rows) => {
// `rows` is an array of rows
// each row being an array of cells.
})
})
Node.js
const readXlsxFile = require('read-excel-file/node');
// File path.
readXlsxFile('/path/to/file').then((rows) => {
// `rows` is an array of rows
// each row being an array of cells.
})
// Readable Stream.
readXlsxFile(fs.createReadStream('/path/to/file')).then((rows) => {
...
})
Dates
XLSX format has no dedicated "date" type so dates are stored internally as simply numbers along with a "format" (e.g. "MM/DD/YY"
). When using readXlsx()
with schema
parameter all dates get parsed correctly in any case. But if using readXlsx()
without schema
parameter (to get "raw" data) then this library attempts to guess whether a cell value is a date or not by examining the cell "format" (e.g. "MM/DD/YY"
), so in most cases dates are detected and parsed automatically. For exotic cases one can pass an explicit dateFormat
parameter (e.g. "MM/DD/YY"
) to instruct the library to parse numbers with such "format" as dates:
readXlsxFile(file, { dateFormat: 'MM/DD/YY' })
JSON
To convert rows to JSON pass schema
option to readXlsxFile()
. It will return { rows, errors }
object instead of just rows
.
// An example *.xlsx document:
// -----------------------------------------------------------------------------------------
// | START DATE | NUMBER OF STUDENTS | IS FREE | COURSE TITLE | CONTACT | STATUS |
// -----------------------------------------------------------------------------------------
// | 03/24/2018 | 10 | true | Chemistry | (123) 456-7890 | SCHEDULED |
// -----------------------------------------------------------------------------------------
const schema = {
'START DATE': {
prop: 'date',
type: Date
// Excel stores dates as integers.
// E.g. '24/03/2018' === 43183.
// Such dates are parsed to UTC+0 timezone with time 12:00 .
},
'NUMBER OF STUDENTS': {
prop: 'numberOfStudents',
type: Number,
required: true
},
// 'COURSE' is not a real Excel file column name,
// it can be any string — it's just for code readability.
'COURSE': {
prop: 'course',
type: {
'IS FREE': {
prop: 'isFree',
type: Boolean
// Excel stored booleans as numbers:
// `1` is `true` and `0` is `false`.
// Such numbers are parsed to booleans.
},
'COURSE TITLE': {
prop: 'title',
type: String
}
}
},
'CONTACT': {
prop: 'contact',
required: true,
type: (value) => {
const number = parsePhoneNumber(value)
if (!number) {
throw new Error('invalid')
}
return number
}
},
'STATUS': {
prop: 'status',
type: String,
oneOf: [
'SCHEDULED',
'STARTED',
'FINISHED'
]
}
}
readXlsxFile(file, { schema }).then(({ rows, errors }) => {
// `errors` have shape `{ row, column, error, value }`.
errors.length === 0
rows === [{
date: new Date(2018, 2, 24),
numberOfStudents: 10,
course: {
isFree: true,
title: 'Chemistry'
},
contact: '+11234567890',
status: 'SCHEDULED'
}]
})
If no type
is specified then the cell value is returned "as is".
There are also some additional exported type
s:
-
Integer
for parsing integerNumber
s. -
URL
for parsing URLs. -
Email
for parsing email addresses.
A schema entry for a column may also define an optional validate(value)
function for validating the parsed value: in that case, it must throw
an Error
if the value
is invalid.
The convertToJson()
function is also exported as a standalone one from read-excel-file/schema
import convertToJson from "read-excel-file/schema"
// `data` is an array of rows, each row being an array of cells.
// `schema` is a "to JSON" convertion schema (see above).
const objects = convertToJson(data, schema)
Map
Sometimes, a developer might want to use some other (more advanced) solution for schema parsing and validation (like yup
). If a developer passes a map
instead of a schema
to readXlsxFile()
, then it would just map each data row to a JSON object without doing any parsing or validation.
// An example *.xlsx document:
// ------------------------------------------------------------
// | START DATE | NUMBER OF STUDENTS | IS FREE | COURSE TITLE |
// ------------------------------------------------------------
// | 03/24/2018 | 10 | true | Chemistry |
// ------------------------------------------------------------
const map = {
'START DATE': 'date',
'NUMBER OF STUDENTS': 'numberOfStudents',
'COURSE': {
'course': {
'IS FREE': 'isFree',
'COURSE TITLE': 'title'
}
}
}
readXlsxFile(file, { map }).then(({ rows }) => {
rows === [{
date: new Date(2018, 2, 24),
numberOfStudents: 10,
course: {
isFree: true,
title: 'Chemistry'
}
}]
})
Displaying schema errors
A React component for displaying schema parsing/validation errors could look like this:
import { parseExcelDate } from 'read-excel-file'
function ParseExcelError({ children: error }) {
// Get a human-readable value.
let value = error.value
if (error.type === Date) {
value = parseExcelDate(value).toString()
}
// Render error summary.
return (
<div>
<code>"{error.error}"</code>
{' for value '}
<code>"{value}"</code>
{' in column '}
<code>"{error.column}"</code>
{error.type && ' of type '}
{error.type && <code>"{error.type.name}"</code>}
{' in row '}
<code>"{error.row}"</code>
</div>
)
}
Transforming rows/columns before schema is applied
When using a schema
there's also an optional transformData(data)
parameter which can be used for the cases when the spreadsheet rows/columns aren't in the correct format. For example, the heading row may be missing, or there may be some purely presentational or empty rows. Example:
readXlsxFile(file, {
schema,
transformData(data) {
// Adds header row to the data.
return [['ID', 'NAME', ...]].concat(data)
// Removes empty rows.
return data.filter(row => row.filter(column => column !== null).length > 0)
}
})
TypeScript
See testing index.d.ts
.
Browser compatibility
Node.js *.xlxs
parser uses xpath
and xmldom
packages for XML parsing. The same packages could be used in a browser because all modern browsers (except IE 11) have native DOMParser
built-in which could is used instead (meaning smaller footprint and better performance) but since Internet Explorer 11 support is still required the browser version doesn't use the native DOMParser
and instead uses xpath
and xmldom
packages for XML parsing just like the Node.js version.
Gotchas
Formulas
Dynamically calculated cells using formulas (SUM
, etc) are not supported.
Advanced
By default it reads the first sheet in the document. If you have multiple sheets in your spreadsheet then pass either sheet: number
(sheet index, starting from 1
) or sheet: string
(sheet name) as part of the options
argument (options.sheet
is 1
by default):
readXlsxFile(file, { sheet: 2 }).then((data) => {
...
})
readXlsxFile(file, { sheet: 'Sheet1' }).then((data) => {
...
})
To get the list of sheets one can pass getSheets: true
option:
readXlsxFile(file, { getSheets: true }).then((sheets) => {
// sheets === [{ name: 'Sheet1' }, { name: 'Sheet2' }]
})
CDN
One can use any npm CDN service, e.g. unpkg.com or jsdelivr.net
<script src="https://unpkg.com/[email protected]/bundle/read-excel-file.min.js"></script>
<script>
var input = document.getElementById('input')
input.addEventListener('change', function() {
readXlsxFile(input.files[0]).then(function() {
// `rows` is an array of rows
// each row being an array of cells.
})
})
</script>
References
For XML parsing xmldom
and xpath
are used.