The code `let hostname` declares a variable called `hostname` in...

The code let hostname declares a variable called hostname in JavaScript. Here is a breakdown of what it does:

1. let keyword: This is used to declare a block-scoped variable in JavaScript. It means the variable will be accessible only within the block (or scope) in which it is defined.

2. Variable name hostname: This is the identifier for the variable.

3. No assignment: Because there's no value assigned to hostname, the variable will be initialized with the value undefined by default.

So, this code essentially declares a variable named hostname with an initial value of undefined. It does not perform any other operation or assign a specific value to it.