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.