Javascript Export Array To CSV File (Simple Examples)

Welcome to a quick tutorial and examples on how to export an array to a CSV file in Javascript. Need to create a CSV file in your web app? Well, we don’t actually need to send the array to the server. Modern Javascript is fully capable of generating files on the client side – Read on for the examples!

 

 

TLDR – QUICK SLIDES

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TABLE OF CONTENTS

 

 

 

HOW CSV FILES WORK

Job,job@doe.com,123456,
Joe,joe@doe.com,234567,
"Joi, Doe",joi@doe.com,345678,

Before we start, here is a quick piece of information for those who are new – CSV files are nothing but simple text files.

• , Columns are separated with commas.
• \r\n Rows are separated with newlines.
• "CELL, WITH COMMA" If a cell contains commas, the value will be enclosed in double-quotes.

 

METHOD 1) BLOB OBJECT DOWNLOAD

1A) THE HTML

<!-- (A) JS -->
<script src="csv.min.js"></script>
<script src="1-blob-download.js"></script>
 
<!-- (B) DOWNLOAD AS CSV -->
<input type="button" value="Demo" onclick="saveCSV()">

1. To simplify “convert array to CSV”, we will be using a lightweight library called csv.js.
2. Just a button to start the demo.

 

1B) THE JAVASCRIPT

function saveCSV () {
  // (A) ARRAY OF DATA
  var array = [
    ["Job", "job@doe.com", "123456"],
    ["Joe", "joe@doe.com", "234567"],
    ["Joi", "joi@doe.com", "345678"],
    ["Jon", "jon@doe.com", "456789"],
    ["Jou", "jou@doe.com", "987654"],
    ["Joy, Doe", "joy@doe.com", "876543"],
  ];
 
  // (B) CREATE BLOB OBJECT
  var blob = new Blob([CSV.serialize(array)], {type: "text/csv"});
 
  // (C) CREATE DOWNLOAD LINK
  var url = window.URL.createObjectURL(blob);
  var anchor = document.createElement("a");
  anchor.href = url;
  anchor.download = "demo.csv";
 
  // (D) "FORCE DOWNLOAD"
  // NOTE: MAY NOT ALWAYS WORK DUE TO BROWSER SECURITY
  // BETTER TO LET USERS CLICK ON THEIR OWN
  anchor.click();
  window.URL.revokeObjectURL(url);
  anchor.remove();
}

Not going to explain this line-by-line, it should be pretty straightforward once you read through the code:

1. var array A nested array of dummy users.
2. new Blob([CSV.serialize(array)], {type: "text/csv"}) creates the CSV file. For the uninitiated, Blob is a “raw binary object”.
3. Due to security restrictions, client-side Javascript cannot directly save the CSV Blob. Thus this entire “roundabout method” of creating a download link.
4. Lastly, offer the CSV file as a download.

 

 

METHOD 2) FILE STREAM

2A) THE HTML

<!-- (A) JS -->
<script src="csv.min.js"></script>
<script src="2-file-stream.js"></script>
 
<!-- (B) DOWNLOAD AS CSV -->
<input type="button" value="Demo" onclick="saveCSV()">

Same old story, we are using csv.js to generate the CSV file.

 

2B) THE JAVASCRIPT

async function saveCSV () {
  // (A) ARRAY OF DATA
  var array = [
    ["Job", "job@doe.com", "123456"],
    ["Joe", "joe@doe.com", "234567"],
    ["Joi", "joi@doe.com", "345678"],
    ["Jon", "jon@doe.com", "456789"],
    ["Jou", "jou@doe.com", "987654"],
    ["Joy, Doe", "joy@doe.com", "876543"],
  ];
 
  // (B) CREATE BLOB OBJECT
  var blob = new Blob([CSV.serialize(array)], {type: "text/csv"});
 
  // (C) FILE HANDLER & FILE STREAM
  const fileHandle = await window.showSaveFilePicker({
    suggestedName : "demo.csv",
    types: [{
      description: "CSV file",
      accept: {"text/csv": [".csv"]}
    }]
  });
  const fileStream = await fileHandle.createWritable();
 
  // (D) WRITE FILE
  await fileStream.write(blob);
  await fileStream.close();
}

But in this example, we are using an alternative way to save the generated CSV file, by creating a writable file stream.

• (A & B) var array, blob The same nested array of dummy users and “CSV blob”.
• (C) The difference here is that we use Javascript to programmatically open a “save file as” window.
  • const fileHandle = await window.showSaveFilePicker() Open a “save as” dialog box.
  • const fileStream = await fileHandle.createWritable() Create a file stream to the user’s chosen file.
• (D) fileStream.write(blob) Write the CSV file.

P.S. Take note that “open save as window” is not supported on all browsers at the time of writing. See the “compatibility checks below”.

 

 

 

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EXAMPLE CODE DOWNLOAD

Click here for the source code on GitHub gist, just click on “download zip” or do a git clone. I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

 

 

LIMITATIONS

As you can see, we are writing an entire “CSV string” into a blob object. This works fine if you don’t have too many entries to deal with, but it will run into memory and performance issues with massive data. While it is possible to write “line-by-line” with the file stream method, it is not fully supported in all browsers.

 

COMPATIBILITY CHECKS

• Arrow Functions – CanIUse
• Show Save File Picker – CanIUse
• Create Writable – CanIUse

At the time of writing, the file stream method will not work on Firefox.

 

LINKS & REFERENCES

• Create & Save Files In Javascript – Code Boxx
• Javascript Read CSV Files Into Array/Object – Code Boxx

 

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