Node.js unset environment variable

The problem is that:

console.log('xx' + process.env.MYVAR + 'xx');

Is actually incorrect. The value of an undefined property is undefined. process.env.MYVAR = undefined is the same as delete process.env.MYVAR in so far as the value of the property is the same. But properties also have a presence that delete removes, in that the key will not show up in the Array returned by Object.keys.

If you want the empty string, instead you must write:

console.log('xx' + (process.env.MYVAR || '') + 'xx');

There is another unintuitive aspect to it: Node.js converts undefined to the string "undefined" when assigning an environment variable:

> process.env.MYVAR = undefined
undefined
> typeof process.env.MYVAR
'string'

You can work around this using delete:

> delete process.env.MYVAR
true
> typeof process.env.MYVAR
'undefined'

Tested with Node.js 10.18, 12.14, 13.5 and 16.15.

For this reason (process.env.MYVAR || '') does not help, as it evaluates to ('undefined' || '').