doc: update example of using await in REPL

Clarify that the lexical scope of `const` is
invalidated when using top-level `await` in REPL.

As part of this change also add tests for the
documented behavior

Fixes: #45918

Co-authored-by: Antoine du Hamel <[email protected]>
Co-authored-by: Dario Piotrowicz <[email protected]>
PR-URL: #57653
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>

Author: dario-piotrowicz

doc/api/repl.md

@@ -258,8 +258,7 @@ undefined
 ```
 
 One known limitation of using the `await` keyword in the REPL is that
-it will invalidate the lexical scoping of the `const` and `let`
-keywords.
+it will invalidate the lexical scoping of the `const` keywords.
 
 For example:
 
@@ -268,10 +267,11 @@ For example:
 undefined
 > m
 123
-> const m = await Promise.resolve(234)
-undefined
-> m
+> m = await Promise.resolve(234)
 234
+// redeclaring the constant does error
+> const m = await Promise.resolve(345)
+Uncaught SyntaxError: Identifier 'm' has already been declared
 ```
 
 [`--no-experimental-repl-await`][] shall disable top-level await in REPL.

test/parallel/test-repl-top-level-await.js

@@ -173,6 +173,12 @@ async function ordinaryTests() {
       '3',
       'undefined',
     ]],
+    // Testing documented behavior of `const`s (see: https://github.com/nodejs/node/issues/45918)
+    ['const k = await Promise.resolve(123)'],
+    ['k', '123'],
+    ['k = await Promise.resolve(234)', '234'],
+    ['k', '234'],
+    ['const k = await Promise.resolve(345)', "Uncaught SyntaxError: Identifier 'k' has already been declared"],
     // Regression test for https://github.com/nodejs/node/issues/43777.
     ['await Promise.resolve(123), Promise.resolve(456)', 'Promise {', { line: 0 }],
     ['await Promise.resolve(123), await Promise.resolve(456)', '456'],