Is there a way to combine text files using the Windows command line?

You can also use the copy command, eg

copy *.js bigfile.txt

or, for specific files

copy file1.txt+file2.txt+file3.txt bigfile.txt

type * > someotherpath/all.txt

The need for creating the file somewhere else is that if the new file is created on the same folder, it should be excluded from the selection.

Also, filtering by extension and using a different one for the resulting file would work. For example:

type *.js > all.txt