[Docs] `process.loadEnvFile()` does not document behaviour when variables already exist

[lonix1]

Affected URL(s)

https://nodejs.org/docs/latest/api/process.html#processloadenvfilepath

Description of the problem

The documentation for process.loadEnvFile(path) states that the .env file is loaded into process.env, but does not document what happens when a variable already exists in process.env.

The --env-file documentation states that an existing environment variable takes precedence over a value from the file.

process.loadEnvFile() appears to have the same behaviour, but this is not stated in its API documentation.

Please document the precedence behaviour for process.loadEnvFile(), for example:

If a variable is already defined in process.env, its existing value takes precedence and is not overwritten by the value from the .env file.