The only way I've been able to get Flow to be usable on my low-specced laptop is to tell it to [ignore] node_modules/.* and add a file to both [ignore] and [libs] which has one of these for each of my dependencies:

    declare module 'npm-module-name' {  declare var exports: any;  }

I needed similar for TypeScript when trying to use noImplicitAny: false - adding "typeRoots": ["node_modules/@types"] in compilerOptions and a d.ts file with the following listed in "files":

    declare module "*"

Typechecking third-party dependencies seems to be a bit of a crapshoot if you're not in a part of the module ecosystem where the tool you're using is either quasi-required, popular or has module authors using the same tool and shipping type definitions themselves. I've had contributed type definitions in both Flow and TypeScript "break" working, tested code.

Typescript is different - I can use type definitions from NPM without typechecking dependencies I don't import.