Bootstrap 4 TypeScript Type Definition fails to compile - Cannot find module 'popper.js'

Two options for you:

• remove the "module": "amd" configuration option OR
• add the "moduleResolution": "node" option.

The second option looks like this:

"moduleResolution": "node",
"module": "amd",

Why do these options work?

In short, when we use amd modules, the default module resolution strategy is Classic as opposed to Node. The important difference between the two is that the Node strategy recognizes directory names as modules whereas the Classic strategy does not.

There is more information on module resolution strategies here.