Node.js: Double '/' characters are loaded from .env file

I am trying to use .env file in my Node.js backend. It has Firebase credentials as the environment variables.

privateKey=-----BEGIN PRIVATE KEY-----\nMIIEvwIBADANBgkqhk

But when I run the Node.js codes, process.env.privateKey is privateKey: '-----BEGIN PRIVATE KEY-----\\nMIIEvwIBADANBgkqh.
Finally double '\' characters are loaded.
A single '\' character should be loaded.
How can I resolve this issue?

via Ilya Shamshudinov