Where does “Janie” come from?

Janie is an English diminutive formation ultimately derived from Proto-Indo-European -kos, a suffix that formed agent nouns and adjectives, passing through Latin -ia and -ivus, Middle French -ie, French -e, and English jane before receiving the English diminutive suffix -ie.

Ancestry of “Janie”, step by step

Step	Language	Word	Meaning
1	English	Jane	A woman, often specifically a girlfriend;...
2	French	Jeanne	Jane, feminine of John
3	Old French	Jehane	—
4	Medieval Latin	Johanna	—
5	Latin	Joanna	—
6	Ancient Greek	Ἰωάννα	—
7	Hebrew	יוֹחָנָה	—
8	Hebrew	יוֹחָנָן	God is gracious
9	Hebrew	יְהוֹחָנָן	God is gracious

Every word from Hebrew יְהוֹחָנָן →Every word from Hebrew יוֹחָנָן →Every word from Hebrew יוֹחָנָה →