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@nextnpm 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!

Prologue

Buffer is part of the Node.js API. Because TypeScript doesn't know classes from Node.js by default, you will need to install declaration files (type definitions) for Node.js.

If you see the following error, you will have to install type definitions manually:

error TS2304: Cannot find name 'Buffer'.

Installing Type Definitions

You can install type definitions using the typings tool. I will show you how to do this:

1. Install the typings tool with npm:

   npm install -g typings

2. Install type definitions for Node.js from the DefinitelyTyped (~dt) repository:

   typings install dt~node --global --save

The typings tool will create the following directory "typings/globals/node" and link it in "typings/index.d.ts". There will be also a file called typings.json (because of the --save option), which references the resolved type definitions:

{  "globalDependencies": {    "node": "registry:dt/node#6.0.0+20160621231320"  }}

Note: If you see the error "typings\globals\node\index.d.ts(71,26): error TS1110: Type expected", then your Node.js definition is too recent. The typings tool has issues with latest type declarations. In such a case, just check the version in your typings.json file. For me node#6.0.0+20160621231320 was working but node#6.0.0+20161212163245 was not.

3. Now all you have to do is adding index.d.ts as a triple-slash directive within your code (which uses the Buffer class):

YourClass.ts

/// <reference path="../../typings/index.d.ts" />export class YourClass {  private static toString(encoded: string): string {    return new Buffer(encoded, "base64").toString();  }}

UPDATE:

With the release of TypeScript 2.0 a new type definitions system has been announced.

You can now forget about the typings tool. All you need to do is running this command to install TypeScript definitions for Node.js:

npm install --save @types/node

Please also make sure that you have the following entries in your tsconfig.json:

{  "compilerOptions": {    "moduleResolution": "node",    ...  },  "exclude": [    "node_modules",    ...  ]}

P.S. If you need type definitions for other classes (than included in Node.js), you can search for them here: http://microsoft.github.io/TypeSearch/