5 Ways To Create & Save Files In Javascript (Simple Examples)

Welcome to a tutorial on how to create and save files in Javascript. Well, this will be kind of a complicated process for beginners. To keep things simple – Saving files on the server-side NodeJS is a breeze, but it is tricky to directly save files on the client side because of security restrictions. That said, there are many methods we can use.

That covers the basics, but let us walk through detailed examples in this tutorial – Read on!

 

 

TLDR – QUICK SLIDES

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TABLE OF CONTENTS

 

 

 

METHOD 1) USE FILE SAVER

<!-- (A) LOAD FILE SAVER -->
<!-- https://cdnjs.com/libraries/FileSaver.js -->
<!-- https://github.com/eligrey/FileSaver.js -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/FileSaver.js/2.0.5/FileSaver.min.js"></script>
 
<script>
// (B) "SAVE AS"
var myFile = new File(["CONTENT"], "demo.txt", {type: "text/plain;charset=utf-8"});
saveAs(myFile);
</script>

Thank goodness, someone did all the hard work. This is one of the easiest and “safest” cross-browser ways to save a file –

1. Simply load FileSaver.js from the CDN.
2. Create a new File() object and pop it into saveAs().

 

 

METHOD 2) CREATE FILE FROM BLOB & FORCE DOWNLOAD

// (A) CREATE BLOB OBJECT
var myBlob = new Blob(["CONTENT"], {type: "text/plain"});

// (B) CREATE DOWNLOAD LINK
var url = window.URL.createObjectURL(myBlob);
var anchor = document.createElement("a");
anchor.href = url;
anchor.download = "demo.txt";
 
// (C) "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);
document.removeChild(anchor);

Due to security restrictions, client-side Javascript cannot directly access the file system. That is, no direct writing and loading of files on the user’s computer. But this is the roundabout way of doing things – Create a BLOB (binary) object to contain all the data, then set a download link to it.

 

METHOD 3) UPLOAD BLOB TO SERVER

THE JAVASCRIPT

<script>
function blobajax () {
  // (A) CREATE BLOB OBJECT
  var myBlob = new Blob(["CONTENT"], {type: "text/plain"});

  // (B) FORM DATA
  var data = new FormData();
  data.append("upfile", myBlob);

  // (C) AJAX UPLOAD TO SERVER
  fetch("3b-upload.php", { method: "POST", body: data })
  .then(res => res.text())
  .then(txt => console.log(txt));
}
</script>
<input type="button" value="Go" onclick="blobajax()">

 

THE PHP

<?php
echo move_uploaded_file(
  $_FILES["upfile"]["tmp_name"], 
  "demo.txt"
) ? "OK" : "ERROR UPLOADING";

This is an alternative to the above BLOB download – We upload the BLOB and save it on the server instead.

 

 

METHOD 4) WRITABLE FILE STREAM

<script>
async function saveFile() {
  // (A) CREATE BLOB OBJECT
  var myBlob = new Blob(["CONTENT"], {type: "text/plain"});
 
  // (B) FILE HANDLER & FILE STREAM
  const fileHandle = await window.showSaveFilePicker({
    types: [{
      description: "Text file",
      accept: {"text/plain": [".txt"]}
    }]
  });
  const fileStream = await fileHandle.createWritable();
 
  // (C) WRITE FILE
  await fileStream.write(myBlob);
  await fileStream.close();
}
</script>
<input type="button" value="Save File" onclick="saveFile()">

Yes, the old grandmother’s age of the Internet is over. We can create a file handler and file stream on the user’s computer, use it to save a file. But this still opens a “save file as” dialog box, we cannot directly save without the user’s permission.

P.S. This will only work on Chrome, Edge, and Opera at the time of writing.

 

METHOD 5) WRITE TO FILE IN NODEJS

// (A) LOAD FILE SYSTEM MODULE
// https://nodejs.org/api/fs.html
const fs = require("fs");

// (B) WRITE TO FILE
fs.writeFile("demo.txt", "CONTENT", "utf8", (error, data) => {
  console.log("Write complete");
  console.log(error);
  console.log(data);
});

/* (C) READ FROM FILE
fs.readFile("demo.txt", "utf8", (error, data) => {
  console.log("Read complete");
  console.log(error);
  console.log(data);
});
*/

Yes, it’s that stupidly simple. Just load the file system module var fs = require("fs"), and use the writeFile() function. To load files, we use the corresponding readFile() function.

 

 

 

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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.

 

 

COMPATIBILITY CHECKS

• Blob – CanIUse
• Create Writable File Stream – CanIUse
• Show Save File Picker – CanIUse
• Arrow Function – CanIUse

Not all browsers support the BLOB data type nor all the file writing features. So it is best to do some checks before you enable your ninja features – I will recommend using Modernizr to detect if the browser supports certain features.

 

LINKS & REFERENCES

• Javascript Blob – MDN
• MIME Types – SitePoint
• Create Object URL and Revoke Object URL – MDN
• Form Data  – MDN
• Fetch API – MDN
• Write Files In NodeJS – Code Boxx

 

TUTORIAL VIDEO

 

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