minor fixes

Author: iliakan

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

@@ -234,12 +234,13 @@ Now let's cover methods that search in an array.
 
 ### indexOf/lastIndexOf and includes
 
-The methods [arr.indexOf](mdn:js/Array/indexOf), [arr.lastIndexOf](mdn:js/Array/lastIndexOf) and [arr.includes](mdn:js/Array/includes) have the same syntax and do essentially the same as their string counterparts, but operate on items instead of characters:
+The methods [arr.indexOf](mdn:js/Array/indexOf) and [arr.includes](mdn:js/Array/includes) have the similar syntax and do essentially the same as their string counterparts, but operate on items instead of characters:
 
 - `arr.indexOf(item, from)` -- looks for `item` starting from index `from`, and returns the index where it was found, otherwise `-1`.
-- `arr.lastIndexOf(item, from)` -- same, but looks for from right to left.
 - `arr.includes(item, from)` -- looks for `item` starting from index `from`, returns `true` if found.
 
+Usually these methods are used with only one argument: the `item` to search. By default, the search is from the beginning.
+
 For instance:
 
 ```js run
@@ -249,27 +250,34 @@ alert( arr.indexOf(0) ); // 1
 alert( arr.indexOf(false) ); // 2
 alert( arr.indexOf(null) ); // -1
 
-let fruits = ['Plum', 'Apple', 'Orange', 'Plum']
-// note that the lastIndexOf method looks for from the end, but index counted from beginning
-alert( fruits.lastIndexOf(Plum)) // 3
-
 alert( arr.includes(1) ); // true
 ```
 
-Note that the methods use `===` comparison. So, if we look for `false`, it finds exactly `false` and not the zero.
+Please note that `indexOf` uses the strict equality `===` for comparison. So, if we look for `false`, it finds exactly `false` and not the zero.
+
+If we want to check if `item` exists in the array, and don't need the exact index, then `arr.includes` is preferred.
+
+The method [arr.lastIndexOf](mdn:js/Array/lastIndexOf) is the same as `indexOf`, but looks for from right to left.
+
+```js run
+let fruits = ['Apple', 'Orange', 'Apple']
 
-If we want to check for inclusion, and don't want to know the exact index, then `arr.includes` is preferred.
+alert( arr.indexOf('Apple') ); // 0 (first Apple)
+alert( arr.lastIndexOf('Apple') ); // 2 (last Apple)
+```
 
-Also, a minor, but noteworthy feature of `includes` is that it correctly handles `NaN`, unlike `indexOf/lastIndexOf`:
+````smart header="The `includes` method handles `NaN` correctly"
+A minor, but noteworthy feature of `includes` is that it correctly handles `NaN`, unlike `indexOf`:
 
 ```js run
 const arr = [NaN];
-alert( arr.indexOf(NaN) ); // -1 (should be 0, but equality test === doesn't work for NaN)
+alert( arr.indexOf(NaN) ); // -1 (wrong, should be 0)
 alert( arr.includes(NaN) );// true (correct)
 ```
+That's because `includes` was added to JavaScript much later and uses the more up to date comparison algorithm internally.
+````
 
-
-### find and findIndex
+### find and findIndex/findLastIndex
 
 Imagine we have an array of objects. How do we find an object with the specific condition?
 
@@ -309,7 +317,28 @@ In real life arrays of objects is a common thing, so the `find` method is very u
 
 Note that in the example we provide to `find` the function `item => item.id == 1` with one argument. That's typical, other arguments of this function are rarely used.
 
-The [arr.findIndex](mdn:js/Array/findIndex) method is essentially the same, but it returns the index where the element was found instead of the element itself and `-1` is returned when nothing is found.
+The [arr.findIndex](mdn:js/Array/findIndex) method has the same syntax, but returns the index where the element was found instead of the element itself. The value of `-1` is returned if nothing is found.
+
+The [arr.findLastIndex](mdn:js/Array/findLastIndex) method is like `findIndex`, but searches from right to left, similar to `lastIndexOf`.
+
+Here's an example:
+
+```js run
+let users = [
+  {id: 1, name: "John"},
+  {id: 2, name: "Pete"},
+  {id: 3, name: "Mary"},
+  {id: 4, name: "John"}
+];
+
+// Find the index of the first John
+alert(users.findIndex(user => user.name == 'John')); // 0
+
+// Find the index of the last John
+alert(users.findLastIndex(user => user.name == 'John')); // 3
+```
+
+
 
 ### filter