Let's output it using alert:

//+ run
function sayHi() {
  alert( "Hello" );
}

*!*
alert( sayHi ); // shows the function code
*/!*

Note that there are no brackets after sayHi in the last line. The function is not called there.

The code above only shows the string representation of the function, that is it's source code.

[cut]

As the function is a value, we can copy it to another variable:

//+ run no-beautify
function sayHi() {   // (1)
  alert( "Hello" ); 
}

let func = sayHi;    // (2)
func(); // Hello     // (3)

sayHi = null;        // (4)
sayHi();             // error 

1. Function declaration `(1)` creates the function and puts it into the variable `sayHi`"
2. Line `(2)` copies it into variable `func`.

   Please note again: there are no brackets after sayHi. If they were, then the call let func = sayHi() would write a result of sayHi() into func, not the function itself.

3. At the moment `(3)` the function can be called both as `sayHi()` and `func()`.
4. ...We can overwrite `sayHi` easily. As well as `func`, they are normal variables. Naturally, the call attempt would fail in the case `(4)`.

[smart header="A function is an "action value""] Regular values like strings or numbers represent the data.

A function can be perceived as an action.

A function declaration creates that action and puts it into a variable of the given name. Then we can run it via brackets () or copy into another variable. [/smart]