[update] data/treecollection api descriptions

Author: mafanya23

docs/data_collection/api/datacollection_add_method.md

@@ -12,9 +12,9 @@ description: You can explore the add method of DataCollection in the documentati
 Please note that data should be loaded into DataCollection via the `parse()` method. The `add()` method is primarily intended for loading standalone elements or small groups of elements, so its loads data slower than the `parse()` method.
 :::
 
-### Usage
+#### Usage
 
-~~~jsx
+~~~ts
 type Id = string | number; 
 add(newItem: IDataItem | IDataItem[], index?: number): Id | Id[];
 ~~~

docs/data_collection/api/datacollection_changeid_method.md

@@ -12,7 +12,7 @@ description: You can explore the changeId method of DataCollection in the docume
 
 @params:
 - `id: string | number` - the old id of an item
-- `newId?: string | number` - optional, the new id; auto-generated if not set
+- `newId: string | number` - the new id; auto-generated if not set
 - `silent?: boolean` - optional, if set to *true*, the method will be called without triggering events; otherwise, *false*
 
 @example:

docs/data_collection/api/datacollection_getsortingstates_method.md

@@ -8,9 +8,9 @@ description: You can explore the getSortingStates method of DataCollection in th
 
 @short: returns an array of objects with the current parameters of sorting applied to the data
 
-## Usage
+#### Usage
 
-~~~jsx 
+~~~ts 
 interface ISortingState {
     by: string | number, 
     dir: "asc" | "desc", 

docs/data_collection/api/datacollection_group_method.md

@@ -16,9 +16,9 @@ Data grouping isn't intended for working with [`lazyDataProxy`](helpers.md/lazyd
 Grouped data can be serialized. After serialization data is available for rendering and editing as a plain tree-like structure
 :::
 
-## Usage
+#### Usage
 
-~~~jsx {16}
+~~~ts {16}
 type TGroupOrderFunc = (item: IDataItem) => string;
 type TAggregate = "sum" | "count" | "min" | "max" | "avg" | string;
 interface IGroupOrder {

docs/data_collection/api/datacollection_reduce_method.md

@@ -8,13 +8,18 @@ description: You can explore the reduce method of DataCollection in the document
 
 @short: reduces the array to a single value
 
-@signature: {'reduce(callback: (acc: any, IDataItem: any, index: number) => any, acc: any): any;'}
+#### Usage
+
+~~~ts
+type ReduceCallBack<IDataItem, A> = (acc: A, item: IDataItem, index: number) => A;
+reduce<A>(callback: ReduceCallBack<IDataItem, A>, acc: A): A;
+~~~
 
 @params:
 
 - `callback: function` - a function that will be called for each item in the array. The function is called with the following parameters:
     - `acc: any` - the *initialValue*, or the previously returned value of the function
-    - `IDataItem: any` - the current item of a data collection
+    - `item: IDataItem` - the current item of a data collection
     - `index: number` - the index of the item 
 - `acc: any` - a value to be passed to the function as the initial value
 

docs/tree_collection/api/treecollection_getsortingstates_method.md

@@ -8,9 +8,9 @@ description: You can explore the getSortingStates method of TreeCollection in th
 
 @short: returns an array of objects with the current parameters of sorting applied to the data
 
-## Usage
+#### Usage
 
-~~~jsx 
+~~~ts
 interface ISortingState {
     by: string | number, 
     dir: "asc" | "desc", 

docs/tree_collection/api/treecollection_update_method.md

@@ -26,12 +26,12 @@ toolbar.data.update("add_btn", { value:"Add new" });
 Also note, that for correct work of the method the last update of a data collection should be done with the `silent:false` setting applied, for example:
 
 ~~~jsx
-const children = tree.data.findAll({ by: "parent", match: "folder_1" });
-const lastIndex = children.length - 1;
+const itemsForUpdate = [...]; // items { ... }
+const lastIndex = itemsForUpdate.length - 1;
 
-children.forEach((item, index) => {
-    tree.data.update(item.id, {
-        icon: { file: "dxi dxi-file", folder: "dxi dxi-folder" },
+itemsForUpdate.forEach((item, index) => {
+    data.update(item.id, {
+        param: "change param",
     }, index != lastIndex); // the last update isn't silent, as the `silent:false` parameter is set
 });
 ~~~