Uncaught Error: Cannot find module 'web3'

This error occurs when the system is unable to locate the required module 'web3'.

Possible reasons for this error could be:

1. The 'web3' module is not installed: You need to install the 'web3' module before you can use it. You can install it using the following command:
npm install web3

2. The module is not imported correctly: Ensure that you have imported the 'web3' module correctly in your code. You can import it using the following statement:
const Web3 = require('web3');

3. The module is not located in the correct directory: Ensure that the 'web3' module is located in the correct directory. You can check the directory using the following command:
npm list web3

4. The module is not added to package.json: Ensure that the 'web3' module is added to the dependencies in the package.json file. You can do this using the following command:
npm install --save web3

Once you have resolved the above issues, you should be able to import and use the 'web3' module without any errors.