Recursively search for a string in files of specified type:
grep -r --include=\*.js "string to search for" ./path/to/folder
grep -r --include=\*.js --include=*.css "string to search for" ./path/to/folder
Find a file:
find ./where/to/look -type f -name 'file-name'
Find a directory:
find ./where/to/look -type d -name 'directory-name'