javascript blob download with code examples

JavaScript Blob Download with Code Examples

Although web developers use a range of technologies to create web applications and websites, the most widely used one is undoubtedly JavaScript, often abbreviated as JS. One of the critical advantages of JavaScript is its capability to process and manipulate data on the client-side. JavaScript, as a result, comes with various built-in features that enable web developers to accomplish complex operations without relying on third-party libraries or server-side code. One feature that is widely used in JavaScript is downloading files through blobs. This article explores how to download files with JavaScript blobs, including relevant code examples.

Downloading files with JavaScript Blobs

A blob is a chunk of data that can store different types of data, such as text or binary data. The data stored in a blob is usually in the form of a file, and sometimes, the data is created dynamically on the client-side. It is possible to download files with JavaScript Blobs, and the steps to achieve this are straightforward. However, developers must adhere to certain conditions when dealing with blobs, including:

  • The file's data must be stored in a Blob object.
  • The Blob object's MIME type should match the file type downloaded.
  • The Blob object's size should be defined as the content length.

To start downloading a file with a blob, the developer must:

  1. Create a JavaScript function that receives the file's data as a parameter.
  2. Use the Blob constructor function to convert the file's data into a Blob object, as shown below:
let blob = new Blob([fileData], { type: application/pdf’});

In this example, fileData refers to the data to be downloaded, while application/pdf specifies the MIME type and should match the file type downloaded. This example creates a blob for a PDF file.

  1. Create the URL for the blob object as shown below:
let blobUrl = URL.createObjectURL(blob);

This function creates a URL for the blob object, which the user will click to download the file.

  1. Create a link node with the URL, as shown below:
let link = document.createElement(“a”);

This line above creates an anchor element which the link to the file will be created and attached it to the DOM.

  1. Set the link's attributes using the following code:
link.href = blobUrl; = fileName;

In the code snippet above, fileName indicates the name of the file, and it is necessary to set it before attaching the link to the DOM. Finally, the link is ready for download.

  1. Click the link programatically using the following code:;

This code above clicks the link, triggering the file download.

Code example

Consider the following code snippet, which downloads a sample PDF file:

const fileUrl = '';
const fileName = 'sample-pdf-file.pdf';

.then(response => response.blob())
.then(blob => {
  const objUrl = URL.createObjectURL(blob);
  const a = document.createElement('a'); = fileName;
  a.href = objUrl;;

The above code downloads a sample PDF file from the web, converts the file into a blob, creates an anchor element with a download attribute before setting the anchor element's HREF attribute to the blob object URL, followed by clicking the anchor element programatically to trigger the file download.


In conclusion, downloading files with JavaScript blobs offers a straightforward approach to download files within JavaScript. With a handful of lines of code, a developer can create a download link for the user to download the file. It offers developers the freedom to deal with data dynamically and link server-side data with files for download by the client. Developers must adhere to guidelines, such as ensuring the blob MIME matches the file type downloaded, and not forgetting to click the anchor element and set a file name for the user to download.

JavaScript is a versatile programming language that allows developers to build complex web applications that are highly interactive and responsive. In this article, we explored one of the key features of JavaScript, downloading files with Blob.

By using Blob, developers can download different types of files from their web applications such as PDFs, images, videos, and more. The process is simple, as developers need to create a Blob object, define the MIME type and size, and then create a download link for the user.

However, downloading files with JavaScript Blobs is not the only feature that developers use in their web applications. There are several other features available in JavaScript that are highly useful in building responsive web applications.

  1. AJAX

AJAX or Asynchronous JavaScript and XML is a powerful feature of JavaScript that enables the client-side to send HTTP requests to the server and receive data without the need for a page refresh. AJAX enables developers to build highly interactive web applications that perform with the speed and responsiveness similar to desktop applications.

  1. JSON

JSON or JavaScript Object Notation is a lightweight data-interchange format that is easy for humans to read and write. It allows developers to serialize data in a structured format, making it easy for different applications to exchange data in standard formats. JSON is used in a wide range of applications, from simple web applications to big data and machine learning applications.

  1. Event Handling

Event handling is an essential feature of JavaScript that allows developers to build highly interactive and responsive web applications. Event handling triggers an action when a specific event happens on the web page, such as a click, hover, or scroll. Developers use event handling to enhance the user experience and make web applications more responsive.

  1. DOM Manipulation

Document Object Model or DOM manipulation is a technique used to modify the content and structure of a web page dynamically. DOM manipulation enables developers to add, remove, or change the content on the page, and update its design and style.

  1. Form Validation

Form validation is a useful feature of JavaScript that checks the user's input before submitting it to the server. Form validation ensures that the user submits the correct and required information, preventing errors and data loss.

In conclusion, JavaScript is a powerful programming language that offers a broad range of features and capabilities to developers building web applications. From downloading files with Blobs to AJAX, JSON, event handling, DOM manipulation, and form validation, JavaScript has everything necessary to create modern, responsive web applications that meet the needs of users today. By leveraging these features efficiently, developers can create highly interactive and responsive web applications that offer superior user experiences.

Popular questions

  1. What is a Blob in JavaScript?

A Blob is a data structure in JavaScript that allows you to store and manipulate binary or text data. It is used to represent file-like objects in the browser and has properties that define the type and size of the data stored in it.

  1. How do you download files with JavaScript Blobs?

To download files with JavaScript Blobs, you need to first create a Blob object from the file data. Then, create a download link using an anchor element and set its href attribute to the object URL of the Blob. Finally, click the anchor element programmatically to initiate the download.

  1. Can you download files of any type using JavaScript Blobs?

Yes, you can download files of any type using JavaScript Blobs. However, you need to ensure you set the correct MIME type when creating the Blob object to ensure that the file is downloaded correctly.

  1. Do you need any external libraries to download files with JavaScript Blobs?

No, you do not need any external libraries to download files with JavaScript Blobs. The process can be accomplished using vanilla JavaScript.

  1. Can you use JavaScript Blobs to download multiple files at once?

Yes, you can use JavaScript Blobs to download multiple files at once. You would need to create separate Blob objects for each file, then create download links for each, and finally initiate the download of each link in a loop.



My passion for coding started with my very first program in Java. The feeling of manipulating code to produce a desired output ignited a deep love for using software to solve practical problems. For me, software engineering is like solving a puzzle, and I am fully engaged in the process. As a Senior Software Engineer at PayPal, I am dedicated to soaking up as much knowledge and experience as possible in order to perfect my craft. I am constantly seeking to improve my skills and to stay up-to-date with the latest trends and technologies in the field. I have experience working with a diverse range of programming languages, including Ruby on Rails, Java, Python, Spark, Scala, Javascript, and Typescript. Despite my broad experience, I know there is always more to learn, more problems to solve, and more to build. I am eagerly looking forward to the next challenge and am committed to using my skills to create impactful solutions.

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