closure task

Author: iliakan

1-js/06-advanced-functions/03-closure/7-closure-sum/solution.md renamed to 1-js/06-advanced-functions/03-closure/6-closure-sum/solution.md

@@ -0,0 +1,40 @@
+The result is: **error**.
+
+Try running it:
+
+```js run
+let x = 1;
+
+function func() {
+*!*
+  console.log(x); // ReferenceError: Cannot access 'x' before initialization
+*/!*
+  let x = 2;
+}
+
+func();
+```
+
+In this example we can observe the peculiar difference between a "non-existing" and "unitialized" variable.
+
+As you may have read in the article [](info:closure), a variable starts in the "uninitialized" state from the moment when the execution enters a code block (or a function). And it stays uninitalized until the corresponding `let` statement.
+
+In other words, a variable technically exists, but can't be used before `let`.
+
+The code above demonstrates it.
+
+```js
+function func() {
+*!*
+  // the local variable x is known to the engine from the beginning of the function,
+  // but "unitialized" (unusable) until let ("dead zone")
+  // hence the error
+*/!*
+
+  console.log(x); // ReferenceError: Cannot access 'vx before initialization
+
+  let x = 2;
+}
+```
+
+This zone of temporary unusability of a variable (from the beginning of the code block till `let`) is sometimes called the "dead zone".

1-js/06-advanced-functions/03-closure/7-closure-sum/task.md renamed to 1-js/06-advanced-functions/03-closure/6-closure-sum/task.md

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+importance: 4
+
+---
+
+# Is variable visible?
+
+What will be the result of this code?
+
+```js
+let x = 1;
+
+function func() {
+  console.log(x); // ?
+
+  let x = 2;
+}
+
+func();
+```
+
+P.S. There's a pitfall in this task. The solution is not obvious.