fixes

1-js/05-data-types/05-array-methods/article.md

@@ -160,13 +160,13 @@ For instance:
 let arr = [1, 2];
 
 // create an array from: arr and [3,4]
-alert( arr.concat([3, 4])); // 1,2,3,4
+alert( arr.concat([3, 4]) ); // 1,2,3,4
 
 // create an array from: arr and [3,4] and [5,6]
-alert( arr.concat([3, 4], [5, 6])); // 1,2,3,4,5,6
+alert( arr.concat([3, 4], [5, 6]) ); // 1,2,3,4,5,6
 
 // create an array from: arr and [3,4], then add values 5 and 6
-alert( arr.concat([3, 4], 5, 6)); // 1,2,3,4,5,6
+alert( arr.concat([3, 4], 5, 6) ); // 1,2,3,4,5,6
 ```
 
 Normally, it only copies elements from arrays. Other objects, even if they look like arrays, are added as a whole:
@@ -180,7 +180,6 @@ let arrayLike = {
 };
 
 alert( arr.concat(arrayLike) ); // 1,2,[object Object]
-//[1, 2, arrayLike]
 ```
 
 ...But if an array-like object has a special `Symbol.isConcatSpreadable` property, then it's treated as an array by `concat`: its elements are added instead:

2-ui/1-document/11-coordinates/article.md

@@ -69,7 +69,7 @@ As you can see, `x/y` and `width/height` fully describe the rectangle. Derived p
 
 Please note:
 
-- Coordinates may be decimal fractions, such as `10.5`. That's normal, internally browser uses fractions in calculations. We don't have to round them when setting to `style.position.left/top`.
+- Coordinates may be decimal fractions, such as `10.5`. That's normal, internally browser uses fractions in calculations. We don't have to round them when setting to `style.left/top`.
 - Coordinates may be negative. For instance, if the page is scrolled so that `elem` is now above the window, then `elem.getBoundingClientRect().top` is negative.
 
 ```smart header="Why derived properties are needed? Why does `top/left` exist if there's `x/y`?"

2-ui/2-events/01-introduction-browser-events/04-move-ball-field/solution.md

@@ -22,7 +22,7 @@ Then the ball will be positioned relatively to the field:
 }
 ```
 
-Next we need to assign the correct `ball.style.position.left/top`. They contain field-relative coordinates now.
+Next we need to assign the correct `ball.style.left/top`. They contain field-relative coordinates now.
 
 Here's the picture:
 
@@ -36,7 +36,7 @@ To get field-relative `left` coordinate of the click, we can substract the field
 let left = event.clientX - fieldCoords.left - field.clientLeft;
 ```
 
-Normally, `ball.style.position.left` means the "left edge of the element" (the ball). So if we assign that `left`, then the ball edge, not center, would be under the mouse cursor.
+Normally, `ball.style.left` means the "left edge of the element" (the ball). So if we assign that `left`, then the ball edge, not center, would be under the mouse cursor.
 
 We need to move the ball half-width left and half-height up to make it center.