make sure a solution always shows up, use "demo" if exists

1-js/06-advanced-functions/03-closure/6-filter-through-function/solution.md

@@ -14,7 +14,7 @@ alert( arr.filter(inBetween(3, 6)) ); // 3,4,5,6
 
 # Filter inArray
 
-```js run
+```js run demo
 function inArray(arr) {
   return function(x) {
     return arr.includes(x);

1-js/06-advanced-functions/03-closure/8-make-army/solution.md

@@ -55,9 +55,9 @@ function makeArmy() {
 
 As a result, all `shooter` functions get from the outer lexical envrironment the same, last value `i=10`.
 
-The fix can be very simple:
+We can fix it by moving the variable definition into the loop:
 
-```js run
+```js run demo
 function makeArmy() {
 
   let shooters = [];
@@ -80,9 +80,9 @@ army[0](); // 0
 army[5](); // 5
 ```
 
-Now it works correctly, because every time the code block in `for (..) {...}` is executed, a new Lexical Environment is created for it, with the corresponding value of `i`.
+Now it works correctly, because every time the code block in `for (let i=0...) {...}` is executed, a new Lexical Environment is created for it, with the corresponding variable `i`.
 
-So, the value of `i` now lives a little bit closer. Not in `makeArmy()` Lexical Environment, but in the Lexical Environment that corresponds the current loop iteration. A `shooter` gets the value exactly from the one where it was created.
+So, the value of `i` now lives a little bit closer. Not in `makeArmy()` Lexical Environment, but in the Lexical Environment that corresponds the current loop iteration. That's why now it works.
 
 ![](lexenv-makearmy.png)
 
@@ -90,7 +90,6 @@ Here we rewrote `while` into `for`.
 
 Another trick could be possible, let's see it for better understanding of the subject:
 
-
 ```js run
 function makeArmy() {
   let shooters = [];

1-js/06-advanced-functions/09-call-apply-decorators/02-delay/solution.md

@@ -1,6 +1,6 @@
 The solution:
 
-```js
+```js run demo
 function delay(f, ms) {
 
   return function() {
@@ -8,20 +8,25 @@ function delay(f, ms) {
   };
 
 }
+
+let f1000 = delay(alert, 1000);
+
+f1000("test"); // shows "test" after 1000ms
 ```
 
 Please note how an arrow function is used here. As we know, arrow functions do not have own `this` and `arguments`, so `f.apply(this, arguments)` takes `this` and `arguments` from the wrapper.
 
-If we pass a regular function, `setTimeout` would call it without arguments and `this=window` (in-browser), so we'd need to write a bit more code to pass them from the wrapper:
+If we pass a regular function, `setTimeout` would call it without arguments and `this=window` (assuming we're in the browser).
+
+We still can pass the right `this` by using an intermediate variable, but that's a little bit more cumbersome:
 
 ```js
 function delay(f, ms) {
 
-  // added variables to pass this and arguments from the wrapper inside setTimeout
   return function(...args) {
-    let savedThis = this;
+    let savedThis = this; // store this into an intermediate variable
     setTimeout(function() {
-      f.apply(savedThis, args);
+      f.apply(savedThis, args); // use it here
     }, ms);
   };
 

1-js/06-advanced-functions/09-call-apply-decorators/03-debounce/solution.md

@@ -1,6 +1,4 @@
-
-
-```js run no-beautify
+```js demo
 function debounce(f, ms) {
 
   let isCooldown = false;
@@ -18,7 +16,7 @@ function debounce(f, ms) {
 }
 ```
 
-The call to `debounce` returns a wrapper. There may be two states:
+A call to `debounce` returns a wrapper. There may be two states:
 
 - `isCooldown = false` -- ready to run.
 - `isCooldown = true` -- waiting for the timeout.

1-js/06-advanced-functions/09-call-apply-decorators/04-throttle/solution.md

@@ -1,4 +1,4 @@
-```js
+```js demo
 function throttle(func, ms) {
 
   let isThrottled = false,