JS Documentation (#3535)

* Initial JS documentation
* Spelling fix

Co-authored-by: あく <alleteam@gmail.com>

documentation/js/js_dialog.md

@@ -0,0 +1,49 @@
+# js_dialog {#js_dialog}
+
+# Dialog module
+```js
+let dialog = require("dialog");
+```
+# Methods
+
+## message
+Show a simple message dialog with header, text and "OK" button.
+
+### Parameters
+- Dialog header text
+- Dialog text
+
+### Retuns
+true if central button was pressed, false if the dialog was closed by back key press
+
+### Examples:
+```js
+dialog.message("Dialog demo", "Press OK to start");
+```
+
+## custom
+More complex dialog with configurable buttons
+
+### Parameters
+Configuration object with the following fileds:
+- header: Dialog header text
+- text: Dialog text
+- button_left: (optional) left button name
+- button_right: (optional) right button name
+- button_center: (optional) central button name
+
+### Retuns
+Name of pressed button or empty string if the dialog was closed by back key press
+
+### Examples:
+```js
+let dialog_params = ({
+    header: "Dialog header",
+    text: "Dialog text",
+    button_left: "Left",
+    button_right: "Right",
+    button_center: "OK"
+});
+
+dialog.custom(dialog_params);
+```