npm run build error

I've been buildling onto the TimelineJS3 library for a while but suddenly this error appeared when running npm run build

Here is the error I'm getting:

ERROR in ./node_modules/fs-extra/lib/index.js
Module not found: Error: Can't resolve 'fs' in '/Users/emmet/Documents/GitHub/TimelineJS3/node_modules/fs-extra/lib'
@ ./node_modules/fs-extra/lib/index.js 22:11-24
@ ./src/js/core/TimelineConfig.js
@ ./src/js/core/ConfigFactory.js
@ ./src/js/index.js

ERROR in ./node_modules/graceful-fs/graceful-fs.js
Module not found: Error: Can't resolve 'fs' in '/Users/emmet/Documents/GitHub/TimelineJS3/node_modules/graceful-fs'
@ ./node_modules/graceful-fs/graceful-fs.js 1:9-22
@ ./node_modules/fs-extra/lib/fs/index.js
@ ./node_modules/fs-extra/lib/index.js
@ ./src/js/core/TimelineConfig.js
@ ./src/js/core/ConfigFactory.js
@ ./src/js/index.js

ERROR in ./node_modules/jsonfile/index.js
Module not found: Error: Can't resolve 'fs' in '/Users/emmet/Documents/GitHub/TimelineJS3/node_modules/jsonfile'
@ ./node_modules/jsonfile/index.js 5:8-21
@ ./node_modules/fs-extra/lib/json/jsonfile.js
@ ./node_modules/fs-extra/lib/json/index.js
@ ./node_modules/fs-extra/lib/index.js
@ ./src/js/core/TimelineConfig.js
@ ./src/js/core/ConfigFactory.js
@ ./src/js/index.js

It's not buidling the main timeline.js output file because of this

Start by running npm run build and tracing the reported imports from src/js/core/TimelineConfig.js through ConfigFactory.js and src/js/index.js. Compare the build configuration and dependency versions with the expected project setup; done means the build completes and produces the main timeline.js output without the reported module-resolution errors.