ReferenceError: Blob is not defined in JavaScript [Solved]

# ReferenceError: Blob is not defined in JavaScript

The "Blob is not defined" error occurs when the Blob class is used without being imported into a Node.js application.

To solve the error, import the Blob class before using it, e.g. import { Blob } from 'buffer';.

To solve the error, import the Blob class before using it.

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import {Blob} from 'buffer';

const blob = new Blob(['hello world']);
console.log(blob); // 👉️ Blob { size: 11, type: '' }

The Blob class takes 2 parameters:

1. sources - an array to be stored within the Blob
2. options - an object, where we can set the endings to transparent or native (line endings get converted to the platform native line endings). The content-type of the Blob can also be set in the object.

You can modify the sources after the Blob is created.

Here's an example where we explicitly set the content-type of the Blob.

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import {Blob} from 'buffer';

const obj = {name: 'James Doe'};
const blob = new Blob([JSON.stringify(obj, null, 2)], {
  type: 'application/json',
});

console.log(blob); // 👉️ Blob { size: 25, type: 'application/json' }

We constructed a Blob from a JSON string and set its content-type to application/json.

Note that Blob is a globally available class in Node.js starting with version 18.

You can check your version of Node with the node -v command.

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node -v

If you use Node.js version 18+, you can directly use the Blob class without importing it.

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const blob = new Blob(['hello world']);
console.log(blob); // 👉️ Blob { size: 11, type: '' }

# Using the cross-blob module instead

An alternative to using the built-in Blob class is to use the cross-blob npm module.

The module offers cross-platform blob implementation for Node.js and the Web.

You can install cross-blob by running the following command.

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# 👇️ with NPM
npm install cross-blob

# 👇️ with YARN
yarn add cross-blob

Now you can import the Blob class from the package as follows.

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import Blob from 'cross-blob';

const blob = new Blob(['hello world']);
console.log(blob.size); // 👉️ 11

// Global patch (to support external modules like is-blob).
globalThis.Blob = Blob;