Getting error TS2304: Cannot find name 'Buffer'

Add this line at top:

declare const Buffer

and it should compile without errors.

Declarations is required to use node built in libraries or other global objects, you can manually declare it like above.

With new version of Typescript, you can also use official declaration files:

npm i -g typescript@next
npm i --save-dev @types/node

for other libraries, install @types/library_name.

more details: Improve Declaration File Acquisition, The Future of Declaration Files

For the IONIC 4 developers, I installed it using

npm install --save @types/node

When I tried adding "types": ["node"] as shown below

"compilerOptions": {
    "outDir": "./out-tsc/app",
    "types": ["node"]
},

to the

tsconfig.json

it did not work. I had to add the entry to

tsconfig.app.json

Please refer to the following link for relevant documentation.
https://github.com/aws/aws-sdk-js/issues/1271#issuecomment-291658668

Let me know if that worked for you!