Read excel node js

Node.js is an open-source and cross-platform JavaScript runtime environment that can also be used to read from a file and write to a file which can be in txt, ods, xlsx, docx, etc format.

The following example covers how an excel file(.xlsx) file is read from an excel file and then converted into JSON and also to write to it. It can be achieved using a package called xlsx to achieve our goal.

Module Installation: You can install xlsx module using the following command:

npm install xlsx

Note: For the following example, text.xlsx is a dummy data file that has been used.

Filename: test.xlsx 

Sheet 1:

Sheet 2:

So the excel file test.xlsx has 2 sheets, one having Student details and another having lecturer details.

Read Operation Filename: read.js 

Explanation: First, the npm module is included in the read.js file and then the excel file is read into a workbook i.e constant file in the above program.

The number of files in that particular excel file is available in the SheetNames property of the workbook. It can be accessed as follows:

const sheets = file.SheetNames  // Here the value of the sheets will be 2

A for loop is run until the end of the excel file starting from the first page. One of the most important functions used in the code above is the sheet_to_json() function present in the utils module of the xlsx package. It accepts a worksheet object as a parameter and returns an array of JSON objects.

There is a forEach loop which iterates through every JSON object present in the array temp and pushes it into a variable data which would contain all the data in JSON format.

Finally, the data is printed or any other modification can be performed on the array of JSON objects.

Step to run the application:

Run the read.js file using the following command:

node read.js

Output:

Write Operation In the following example, we will convert an array of JSON objects into an excel sheet and append it to the file.

Filename: write.js

Explanation: Here we have an array of JSON objects called student_data. We use two main functions in this program i.e json_to_sheet() which accepts an array of objects and converts them into a worksheet and another function is the book_append_sheet() to append the worksheet into the workbook.

Finally, all the changes are written to the test.xlsx file using writeFile() function which takes a workbook and a excel file as input parameter.

Step to run the application:

Run the read.js file using the following command:

node write.js

Output: The final test.xlsx file would look something like this: 

Sheet 1:

Sheet 2:

Sheet 3: We can see sheet 3 is appended into the test.xlsx as shown below:

This article shows you how to read and extract content from an Excel (.xlsx) file by using Node.js. Without any further ado, let’s get our hands dirty and start coding.

Getting Things Ready

We are going to work with a simple Excel file that contains some information as follows:

You can download the file from the link below to your computer:

https://www.kindacode.com/wp-content/uploads/2021/11/KindaCode.com-Example.xlsx.zip

Writing Code

There are many great libraries that can help us easily read Excel files, such as xlsx (SheetJS), exceljs (ExcelJS), node-xlsx (Node XLSX). In the sample project below, we will use xlsx. It’s super popular and supports TypeScript out-of-the-box.

1. Create a new folder named example (the name doesn’t matter and is totally up to you), then initialize a new Node.js project by running:

npm init

2. In your project directory, create a subfolder called src, then add an empty index.js file. Copy the Excel file you’ve downloaded before into the src folder.

Here’s the file structure:

.
├── node_modules
├── package-lock.json
├── package.json
└── src
    ├── KindaCode.com Example.xlsx
    └── index.js

3. Installing the xlsx package:

npm i xlsx

4. Below are the code snippets for index.js. There are 2 different code snippets. The first one uses the CommonJS syntax (with require), while the second one uses the ES Modules syntax (with import). Choose the one that fits your need.

CommonJS:

const path = require("path");
const xlsx = require("xlsx");

const filePath = path.resolve(__dirname, "Kindacode.com Example.xlsx");

const workbook = xlsx.readFile(filePath);
const sheetNames = workbook.SheetNames;

// Get the data of "Sheet1"
const data = xlsx.utils.sheet_to_json(workbook.Sheets[sheetNames[0]])

/// Do what you need with the received data
data.map(person => {
  console.log(`${person.Name} is ${person.Age} years old`);
})

ES Modules:

// import with ES6 Modules syntax
import path from 'path';
import xlsx from 'xlsx';

import { fileURLToPath } from 'url'
import { dirname } from 'path'
const __filename = fileURLToPath(import.meta.url)
const __dirname = dirname(__filename)

const filePath = path.resolve(__dirname, "Kindacode.com Example.xlsx");

const workbook = xlsx.readFile(filePath);
const sheetNames = workbook.SheetNames;

// Get the data of "Sheet1"
const data = xlsx.utils.sheet_to_json(workbook.Sheets[sheetNames[0]])

/// Do what you need with the received data
data.map(person => {
  console.log(`${person.Name} is ${person.Age} years old`);
})

5. Test our project:

node src/index.js

Output:

John Doe is 37 years old
Jane Doe is 37 years old
Captain is 72 years old
Voldermort is 89 years old

Conclusion

We’ve written a simple Node.js program to retrieve the data from a sheet of an Excel workbook. If you’d like to explore more new and interesting things about modern Node.js, take a look at the following articles:

• Node.js: How to Ping a Remote Server/ Website
• Best open-source ORM and ODM libraries for Node.js
• 7 Best Open-Source HTTP Request Libraries for Node.js
• Node.js: Executing a Piece of Code after a Delay
• Express + TypeScript: Extending Request and Response objects

You can also check out our Node.js category page for the latest tutorials and examples.

My favourite library for reading, writing, and manipulating Excel files in Node.JS is ExcelJS. In this tutorial, we’ll look at how to install the library and how to dynamically read an Excel file.

In the business world, there’s a joke that businesses run off Excel files. Sadly, this can be very true – I’ve received a lot of Excel files over the years and had to do data imports or build visualizations off of them. I’ve used code like we’ll look at today in a lot of applications.

Installing ExcelJS

Installing ExcelJS is pretty easy. In the root of your project, just simply run “npm i exceljs” from the terminal or command prompt.

Setting Up Our Code for ExcelJS

We can import or require ExcelJS by just requiring exceljs. If you need ES5 transpiled code, you’ll need to import ‘exceljs/dist/es5’ instead and add the core-js dependencies too.

In Microsoft Excel, a workbook is a collection of worksheets (or “spreadsheets”) in a single file. In the Microsoft Excel API, operations usually begin from the workbook object.

One thing to keep in mind whenever doing something with Excel, is that everything is one based.

Reading a Particular Worksheet

There’s a few different ways that we can access worksheets. Worksheets can be accessed by iteration, through the Id, or by the worksheet tab name.

I prefer to access worksheets by iteration or by name because these methods are a lot more predictable. When doing By Id or by Number keep in mind that the numbers aren’t necessarily sequential because a worksheet may no longer exist.

Accessing Worksheets Through Iteration

As mentioned above, I find accessing worksheets through iteration to be the easiest and more predictable way of reading an Excel sheet.

With ExcelJS we have a few different ways we can iterate through through the worksheets. We can do it by a for loop, a .forEach off of workbook.worksheets.forEach, or doing workbook.eachSheet.

I find workbook.eachSheet to be the easiest to read.

Build In Metrics

Within ExcelJS, there are a few different variables that we can use to make life easier.

We can use worksheet.actualColumnCount to get the number of columns that potentially have any data in them.

We can use worksheet.actualRowCount to get the size of the rows that potentially have data in them.

As we’re iterating through rows, we can use row.cellCount to get the number of cells.

Reading a Particular Cell

In Excel, a cell is the boxes you see in the grid of an Excel worksheet. Cells are traditionally referenced by the column letter, and row number. For example “A1” is the first cell on an Excel worksheet.

Within ExcelJS, we can also use a number instead of a letter as the column reference. For example “1,1” could also be a reference to “A1”.

If we need the value of the cell, we need to use .getCell() and then use the .value property. Like this:

It’s much easier to use a number as a reference, although it can be confusing when you are comparing the code to a spreadsheet. And of course, when looping this is a lot easier than trying to translate a number to a letter.

Dynamically Reading an Entire Document

When I work with Excel documents in Node.js I like to convert them into a JavaScript array of objects so I can easily manipulate them. So, an Excel document that looks like this will end up looking like this JavaScript array of objects.

I usually start with a helper function that takes in the path to the Excel file, and then it reads it and loops through the various worksheets.

For each worksheet it assumes that the first row is a header row. In a lot of cases, this is a good assumption but it never hurts to check. 😊

For each worksheet, we loop through the rows and and the available columns building an object that we eventually add an object called “theRow” into the “theData” array.

At the end, we return theData which is our array of objects.

Wrapping It Up

As you can see, having a knowledge of loops and the ExcelJS library can allow us to do some pretty advanced things without necessarily having to have a human do a lot of data entry.

In this blog post on ExcelJS we covered how to read in an Excel file and convert it to a JavaScript array that contains objects based on headers built from the first row.