read-excel-file

Read .xlsx files in a browser or Node.js.

It also supports parsing spreadsheet rows into JSON objects using a schema.

Demo

Also check out write-excel-file for writing .xlsx files.

Install

npm install read-excel-file --save

Alternatively, it could be included on a web page directly via a <script/> tag.

Use

If your .xlsx file only has a single "sheet", or if you only need to read a single "sheet", or if you don't care what a "sheet" is, use readSheet() function.

For example, consider the following .xlsx file:

Here's how to read it using readSheet() function:

import { readSheet } from 'read-excel-file/node'

await readSheet(file) ===
[
  ['Name', 'Date of Birth', 'Married', 'Kids'],
  ['John Smith', 1995-01-01T00:00:00.000Z, true, 3],
  ['Kate Brown', 2010-03-01T00:00:00.000Z, false, 0]
]

The result is an array of rows. Each row is an array of values — string, number, boolean or Date.

It also has an optional second argument — sheet — which could be a sheet number (starting from 1) or a sheet name. By default, it reads the first sheet.

But if you need to read all available "sheets" in a file, use the default exported function:

import readExcelFile from 'read-excel-file/node'

await readExcelFile(file) ===
[{
  sheet: 'Sheet1',
  data: [
    ['Name', 'Age'],
    ['John Smith', 30],
    ['Kate Brown', 15]
  ]
}, {
  sheet: 'Sheet2',
  data: ...
}]

The result is a non-empty array of "sheets". Each "sheet" is an object with properties:

• sheet — Sheet name.
  • Example: "Sheet1"
• data — Sheet data. An array of rows. Each row is an array of values — string, number, boolean or Date.
  • Example: [ ['Name','Age'], ['John Smith',30], ['Kate Brown',15] ]

Import

This package provides a separate import path for each different environment, as described below.

Browser

read-excel-file/browser

It can read from a File, a Blob or an ArrayBuffer.

Example: User chooses a file and the web application reads it.

<input type="file" id="input" />

import { readSheet } from 'read-excel-file/browser'

const input = document.getElementById('input')

input.addEventListener('change', () => {
  const data = await readSheet(input.files[0])
})

Note: Internet Explorer 11 is an old browser that doesn't support Promise, and hence requires a polyfill.

const response = await fetch('https://example.com/spreadsheet.xlsx')
const block = await response.blob()
const data = await readSheet(blob)

// Step 1: Initialize Web Worker.

const worker = new Worker('web-worker.js')

worker.onmessage = function(event) {
  // `event.data` is a `File`.
  console.log(event.data)
}

worker.onerror = function(event) {
  console.error(event.message)
}

// Step 2: User chooses a file and the application sends it to the Web Worker.

const input = document.getElementById('input')

input.addEventListener('change', () => {
  worker.postMessage(input.files[0])
})

import { readSheet } from 'read-excel-file/web-worker'

onmessage = async function(event) {
  const sheetData = await readSheet(event.data)
  postMessage(sheetData)
}

Node.js

read-excel-file/node

It can read from a file path, a Stream, a Buffer or a Blob.

Example 1: Read from a file path.

import { readSheet } from 'read-excel-file/node'

const data = await readSheet('/path/to/file')

Example 2: Read from a Stream

import { readSheet } from 'read-excel-file/node'

const data = await readSheet(fs.createReadStream('/path/to/file'))

Universal

read-excel-file/universal

This one works both in a web browser and Node.js. It can only read from a Blob or an ArrayBuffer, which could be a bit less convenient for general use.

import { readSheet } from 'read-excel-file/universal'

const data = await readSheet(blob)

Strings

By default, it automatically trims all string values. To disable this behavior, pass trim: false option.

readExcelFile(file, { trim: false })

Dates

.xlsx file format originally had no dedicated "date" type, so dates are in almost all cases stored simply as numbers, equal to the count of days since 01/01/1900 (with a few quirks). To correctly interpret such numbers as dates, each date cell in an .xlsx file specifies a certain "format" — for example, "d mmm yyyy" — that instructs a spreadsheet viewer application to interpret the numeric value in the cell as a date rather than a number, and display it using the specified format.

Being no different from a generic spreadsheet viewer application, this package follows the same practice: it attempts to guess whether a given cell value is a date or a number by looking at the cell's "format" — if the "format" is one of the known standard date formats then the cell value is interpreted as a date rather than a number. So usually there's no need to configure anything and it usually "just works" out-of-the-box.

Although there's still a possibility for an .xlsx file to specify a totally-custom non-standard date format. In such case, a developer could pass a dateFormat parameter to tell this package to parse cells having that specific "format" as date ones rather than numeric ones: readExcelFile(file, { dateFormat: 'mm/dd/yyyy' }).

Numbers

When reading an .xlsx file, any numeric values are parsed from a string to a javascript number. But there's an inherent issue with javascript numbers in general — their floating-point precision is sometimes less than ideal. For example, 0.1 + 0.2 != 0.3. Yet, applications in areas such as finance or banking usually require 100% floating-point precision, which is usually worked around by using a custom implementation of a "decimal" data type such as decimal.js.

This package supports passing a custom parseNumber(string) function as an option when reading an .xlsx file. By default, it parses a string to a javascript number, but one could pass any custom implementation.

Example: Use "decimal" data type to perform further calculations on fractional numbers with 100% precision.

import Decimal from 'decimal.js'

readExcelFile(file, {
  parseNumber: (string) => new Decimal(string)
})

Formulas

This package doesn't support reading cells that use formulas to calculate the value: SUM, AVERAGE, etc.

Performance

Here're the results of reading sample .xlsx files of different size:

Schema

Oftentimes, the task is not just to read the "raw" spreadsheet data but also to convert each row of that data to a JSON object having a certain structure. Because it's such a common task, this package exports a named function parseSheetData(data, schema) which does exactly that. It parses sheet data into an array of JSON objects according to a pre-defined schema which describes how should a row of data be converted to a JSON object.

import { readSheet, parseSheetData } from "read-excel-file/browser"

const data = await readSheet(file)
const schema = { ... }
const { objects, errors } = parseSheetData(data, schema)
if (errors) {
  console.error(errors)
} else {
  console.log(objects)
}

The parseSheetData() function returns an object — { objects, errors }. Depending on whether there were any errors when parsing the data, either objects or errors property will be undefined.

The sheet data that is being parsed should adhere to a simple structure: the first row should be a header row with just column titles, and each following row should specify the values for those columns.

The schema argument should describe the structure of the resulting JSON objects. An example of a schema is provided at the end of this section.

Specifically, a schema should be an object having the same keys as a resulting JSON object, with values being nested objects having the following properties:

• column — The title of the column to read the value from.
  • If the column is missing from the spreadsheet, the property value will be undefined.
    • This can be overridden by passing propertyValueWhenColumnIsMissing option. Is undefined by default.
  • If the column is present in the spreadsheet but is empty, the property value will be null.
    • This can be overridden by passing propertyValueWhenCellIsEmpty option. Is null by default.
• required — (optional) Is the value required?
  • Could be one of:
    • required: boolean
      • true — The column must not be missing from the spreadsheet and the cell value must not be empty.
      • false — The column can be missing from the spreadsheet, or the cell value can be empty.
    • required: (object) => boolean — A function returning true or false depending on the other properties of the object.
• validate(value) — (optional) Validates the value. Is only called for non-empty cells. If the value is invalid, this function should throw an error.
• schema — (optional) If the value is going to be a nested object, schema should describe that nested object.
  • If when parsing such nested object, all of its property values happen to be empty — undefined or null — then the nested object will be itself set to null.
    • This can be overridden by passing transformEmptyObject(object, { path? }) function as an option. By default, it returns null.
    • This applies both to nested objects and to the top-level object itself.
• type — (optional) If the value is not going to be a nested object, type should describe the type of the value. It will determine how the cell value will be converted to a property value. If no type is specified then the property value will be same as the cell value.
  • Valid types:
    • Standard types:
      • String
      • Number
      • Boolean
      • Date
    • One of the "utility" types that're exported from this package:
      • Integer
      • Email
      • URL
    • Custom type:
      • A function that receives a cell value and returns any kind of a parsed value. Returning undefined will have same effect as returning null. If the value is invalid, it should throw an error.
  • If the cell value is comprised of comma-separated values (example: "a, b, c") and if it should be parsed as an array of such values, then the property type could be specified as an array — type: [elementType] — where elementType could be any valid type described above. For example, if a property is defined as { type: [String] } and the cell value is "a, b, c" then the property value will be parsed as ["a", "b", "c"].
    • If the cell is empty, or if every element of the parsed array is null or undefined, then the property value itself will be set to null.
      • This can be overridden by passing transformEmptyArray(array, { path }) function as an option. By default, it returns null.
    • The separator could be specified by passing arrayValueSeparator option. By default, it's ",".
    • The separated parts of a cell value will be trimmed.

If there're any errors during the conversion process, the errors property returned from the function will be a non-empty array (by default, it's an empty array). Each error object has properties:

• error: string — The error code. Examples: "required", "invalid".
  • If a custom validate() function is defined and it throws a new Error(message) then the error property will be the same as the message argument.
  • If a custom type() function is defined and it throws a new Error(message) then the error property will be the same as the message argument.
• reason?: string — An optional secondary error code providing more details about the error. I.e. "error.error happened specifically because of error.reason". Currently, it could only be returned for the standard types.
  • Example: { error: "invalid", reason: "not_a_number" } for a type: Number property means that "the cell value is invalid because it's not a number".
• row: number — The row number, starting from 1.
  • row: 1 means "first row of data", etc.
  • Don't mind the header row.
• column: string — The column title.
• columnIndex: number — The column index.
  • columnIndex: 0 means "first column", etc.
• value?: any — The cell value.
• type?: any — The type of the property, as defined by the schema.

Example:

// An example .xlsx document:
// --------------------------------------------------------------------------------------------------------
// | START DATE | SEATS |   STATUS  |    CONTACT     | COURSE TITLE  | COURSE CATEGORY   | COURSE IS FREE |
// --------------------------------------------------------------------------------------------------------
// | 03/24/2018 |   10  | SCHEDULED | (123) 456-7890 | Basic Algebra | Math, Arithmetic  |     TRUE       |
// --------------------------------------------------------------------------------------------------------

const schema = {
  startDate: {
    column: 'START DATE',
    type: Date
  },
  seats: {
    column: 'SEATS',
    type: Number,
    required: true
  },
  status: {
    column: 'STATUS',
    type: String,
    // An example of using `oneOf`
    oneOf: [
      'SCHEDULED',
      'STARTED',
      'FINISHED'
    ]
  },
  contact: {
    column: 'CONTACT',
    required: true,
    // An example of using a custom `type`
    type: PhoneNumber
  },
  // Nested object example
  course: {
    // A nested object could be declared as completely optional by specifying `required: false`.
    // In that case, when all of its properties are missing from the input data, it wouldn't throw any error
    // regardless of whether some of its properties are declared as `required: true` or not.
    required: false,
    schema: {
      title: {
        column: 'COURSE TITLE',
        type: String,
        // When course data is present, the course title must be specified.
        required: true
      },
      categories: {
        column: 'COURSE CATEGORY',
        // An example of parsing comma-separated values.
        type: [String]
      },
      isFree: {
        column: 'COURSE IS FREE',
        type: Boolean
      }
    }
  }
}

// If this code was written in TypeScript, `schema` would've been declared as:
// const schema: Schema<Object, ColumnTitle> = { ... }

// Read `data` from an `.xlsx` file
const data = await readSheet(file)

// Parse `data` using a `schema`
const { objects, errors } = parseSheetData(data, schema)

// There have been no errors when parsing the sheet data, so `errors` is `undefined`.
// Should there have been any errors when parsing the sheet data, `errors` would've been
// an array of items having shape: `{ row, column, error, reason?, value?, type? }`.
errors === undefined

// There's one data row in the `.xlsx` file.
objects.length === 1

// The parsed data row.
objects[0] === {
  startDate: new Date(Date.UTC(2018, 3 - 1, 24)),
  seats: 10,
  status: 'SCHEDULED',
  contact: '+11234567890',
  course: {
    title: 'Basic Algebra',
    categories: ['Math', 'Arithmetic']
    isFree: true
  }
}

// An example of a custom `type` parser function.
// It will parse the cell value when it's not empty.
function PhoneNumber(value) {
  const number = parsePhoneNumber(value)
  if (!number) {
    throw new Error('invalid')
  }
  return number
}

import type {
  Schema,
  CellValue,
  ParseSheetDataError,
  ParseSheetDataCustomType,
  ParseSheetDataCustomTypeErrorMessage
} from 'read-excel-file/node'

type ColumnTitle = 'COLUMN TITLE 1' | 'COLUMN TITLE 2'

type CustomTypeValue = string

function CustomType(value: CellValue): CustomTypeValue {
  if (typeof value !== 'string') {
    throw new Error('not_a_string')
  }
  return '~' + value + '~'
}

type CustomTypeErrorMessage<Type extends ParseSheetDataCustomType<unknown>> =
  Type extends typeof CustomType
    ? 'not_a_string'
    : never

// type CustomTypeErrorReason<
//   Type extends ParseSheetDataCustomType<unknown>,
//   ErrorMessage extends ParseSheetDataCustomTypeErrorMessage<Type>
// > =
//   Type extends typeof CustomType
//     ? (ErrorMessage extends 'not_a_string' ? undefined : never)
//     : never

type PossibleError = ParseSheetDataError<
  ColumnTitle,
  typeof CustomType,
  CustomTypeErrorMessage<typeof CustomType>
  // CustomTypeErrorReason<typeof CustomType, CustomTypeErrorMessage<typeof CustomType>>
>

interface Object {
  property1: CustomTypeValue;
  property2?: string;
}

const schema: Schema<Object, ColumnTitle> = {
  property1: {
    column: 'COLUMN TITLE 1',
    type: CustomType,
    required: true
  },
  property2: {
    column: 'COLUMN TITLE 2',
    type: String
  }
}

const { objects, errors } = parseSheetData<Object, ColumnTitle, PossibleError>([
  ['COLUMN TITLE 1', 'COLUMN TITLE 2'],
  ['Value 1', 'Value 2']
], schema)

if (errors) {
  for (const error of errors) {
    console.error('Error in data row', error.row, 'column', error.column, ':', error.error, error.reason || '')
  }
} else {
  console.log('Objects', objects)
}

function ErrorsList({ errors }) {
  return (
    <ul>
      {errors.map((error, i) => (
        <li key={i}>
          <ErrorItem error={error}>
        </li>
      ))}
    </ul>
  )
}

function ErrorItem({ error }) {
  const {
    error: errorMessage,
    reason,
    row,
    column,
    columnIndex,
    value,
    type
  } = error

  // Error summary.
  return (
    <div>
      <code>"{errorMessage}"</code>
      {reason && ' '}
      {reason && <code>("{reason}")</code>}
      {' for value '}
      <code>{stringifyValue(value)}</code>
      {' in column '}
      <code>"{column}"</code>
      {' in data row '}
      <code>{row}</code>
      {' of the spreadsheet'}
    </div>
  )
}

function stringifyValue(value) {
  // Wrap strings in quotes.
  if (typeof value === 'string') {
    return '"' + value + '"'
  }
  return String(value)
}

Browser Support

An .xlsx file is just a .zip archive with an .xslx file extension. This package uses fflate for .zip decompression. See fflate's browser support for further details.

CDN

To include this library directly via a <script/> tag on a page, one can use any npm CDN service, e.g. unpkg.com or jsdelivr.com

<script src="https://unpkg.com/read-excel-file@5.x/bundle/read-excel-file.min.js"></script>

<script>
  var input = document.getElementById('input')
  input.addEventListener('change', function() {
    readXlsxFile(input.files[0]).then(function(rows) {
      // `rows` is an array of rows
      // each row being an array of cells.
    })
  })
</script>

GitHub

On March 9th, 2020, GitHub, Inc. silently banned my account (erasing all my repos, issues and comments, even in my employer's private repos) without any notice or explanation. Because of that, all source codes had to be promptly moved to GitLab. The GitHub repo is now only used as a backup (you can star the repo there too), and the primary repo is now the GitLab one. Issues can be reported in any repo.

License

MIT