diff --git a/1-js/1-getting-started/2-es-modern-now/article.md b/1-js/1-getting-started/2-es-modern-now/article.md
index c582b2de..31913d72 100644
--- a/1-js/1-getting-started/2-es-modern-now/article.md
+++ b/1-js/1-getting-started/2-es-modern-now/article.md
@@ -5,8 +5,14 @@ The [latest standard](http://www.ecma-international.org/publications/standards/E
As it includes a lot of new features, most browsers implement them partially. You can find the current state of the support at [](https://kangax.github.io/compat-table/es6/).
+## Single-engine app
+
If a project is developed for a single JavaScript engine, like V8 (Node.JS, Chrome), then we can use V8-supported features. That's a lot.
+Most notably, V8 supports many of the new features only if the code is running in the "strict mode" (modern mode), which should be enabled explicitly using a directive `'use strict';` at the start.
+
+You will find most code in this tutorial using this directive and, because of that, runnable in Chrome.
+
But what if we're writing a cross-browser application? Different browsers support different subsets of ES-2015.
Here comes Babel.JS.
@@ -68,13 +74,13 @@ That doesn't mean that the example is wrong! It's just the browser lacking the s
[Chrome Canary](https://www.google.com/chrome/browser/canary.html) is recommended, most examples work in it.
-[Firefox Developer Edition](https://www.mozilla.org/en-US/firefox/channel/#developer) is fine too, but it has certain glitches. Like: [let](/let-const) variables working only with when the script type contains `version=1.7` or `1.8`: `
diff --git a/1-js/2-first-steps/11-uibasic/article.md b/1-js/2-first-steps/11-uibasic/article.md
index 381e2cd7..0ba8975b 100644
--- a/1-js/2-first-steps/11-uibasic/article.md
+++ b/1-js/2-first-steps/11-uibasic/article.md
@@ -45,7 +45,7 @@ As with `alert`, the `prompt` window is modal.
```js
//+ run
-var age = prompt('How old are you?', 100);
+let age = prompt('How old are you?', 100);
alert(`You are ${age} years old!`)
```
@@ -57,14 +57,14 @@ Run this code in Internet Explorer to see that:
```js
//+ run
-var test = prompt("Test");
+let test = prompt("Test");
```
So, to look good in IE, it's recommended to always provide the second argument:
```js
//+ run
-var test = prompt("Test", ''); // <-- for IE
+let test = prompt("Test", ''); // <-- for IE
```
[/warn]
@@ -85,7 +85,7 @@ For example:
```js
//+ run
-var isBoss = confirm("Are you the boss?");
+let isBoss = confirm("Are you the boss?");
alert( isBoss ); // true is OK is pressed
```
diff --git a/1-js/2-first-steps/12-ifelse/2-check-standard/ifelse_task2/index.html b/1-js/2-first-steps/12-ifelse/2-check-standard/ifelse_task2/index.html
index b6e3b589..52a68f1d 100644
--- a/1-js/2-first-steps/12-ifelse/2-check-standard/ifelse_task2/index.html
+++ b/1-js/2-first-steps/12-ifelse/2-check-standard/ifelse_task2/index.html
@@ -3,7 +3,9 @@