Update as recommended by @skcat31

snippets/indexesOf.md

@@ -5,15 +5,13 @@ Returns an array of indexes at which the `val` occurs in `arr`. If it occurs onl
 ``` js
 const indexesOf = (arr, val) => {
     let indexes = [], i;
-    for(i = 0; i < arr.length; i++)
-        if (arr[i] === val)
-            indexes.push(i);
-    return indexes.length === 0 ? -1 : indexes.length === 1 indexes.pop() : indexes
+    arr.forEach((el,i) => {if(el === val) indexes.push(i)})
+    return indexes.length === 0 ? [-1] : indexes
 }
 ```
 ``` js
-indexesOf([1,2,3],1); // 0
+indexesOf([1,2,3],1); // [0]
 indexesOf([1,2,3,1,2,3],1); // [0,3]
-indexesOf([1,2,3],4); // -1
-indexesOf([[1,2,3]],[1,2,3]); // -1 (Array.prototype.indexOf()) has the same behaviour
+indexesOf([1,2,3],4); // [-1]
+indexesOf([[1,2,3]],[1,2,3]); // [-1] (Array.prototype.indexOf()) has the same behaviour
 ```