update docs

Signed-off-by: Nannie_wangli <annie.wangli@huawei.com>

en/application-dev/reference/apis/js-apis-filemanager.md

+# Public File Access and Management
+>![icon-note.gif](public_sys-resources/icon-note.gif) **NOTE:**
+>The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
+## Modules to Import
+
+```js
+import filemanager from 'ohos.filemanager';
+```
+
+## System Capabilities
+
+SystemCapability.FileManagement.FileManagerService
+
+## filemanager.getRoot
+
+getRoot(options? : {dev? : DevInfo}) : Promise<FileInfo[]>
+
+Obtains information about the files in the first-level directory in asynchronous mode. This method uses a promise to return the result.
+
+- Parameters
+  | Name| Type| Mandatory| Description|
+  | --- | --- | --- | -- |
+  | dev | [DevInfo](#devinfo) | No| Device name. The default value is **local**, which is the only value supported.|
+
+- Return value
+
+  | Type| Description|
+  | --- | -- |
+  | Promise<[FileInfo](#fileinfo)[]> | Promise used to return the file information obtained.|
+
+- Example
+
+```js
+filemanager.getRoot().then((fileInfo) => {
+    if(Array.isArray(fileInfo)) {
+        for (var i = 0; i < fileInfo.length; i++) {
+            console.log(JSON.Stringify(fileInfo))
+        }
+    }
+}).catch((err) => {
+    console.log(err)
+});
+```
+
+## filemanager.getRoot
+
+getRoot(options? : {dev? : DevInfo}, callback : AsyncCallback&lt;FileInfo[]&gt;) : void
+
+Obtains information about the files in the first-level directory in asynchronous mode. This method uses a callback to return the result.
+
+- Parameters
+
+  | Name| Type| Mandatory| Description|
+  | -------- | ------------------------- | ---- | ----------------------------- |
+  | dev      | [DevInfo](#devinfo)              | No| Device name. The default value is **local**, which is the only value supported.|
+  | callback | AsyncCallback&lt;[FileInfo](#fileinfo)[]&gt; | Yes| Callback invoked to return the file information obtained.|
+
+- Example
+
+```js
+filemanager.getRoot((err, fileInfo) => {
+    if(Array.isArray(fileInfo)) {
+        for (var i = 0; i < fileInfo.length; i++) {
+            console.log(JSON.Stringify(fileInfo))
+        }
+    }
+})
+```
+
+## filemanager.listFile
+
+listFile(path : string, type : string, options? : {dev? : DevInfo, offset? : number, count? : number}) : Promise&lt;FileInfo[]&gt;
+
+Obtains information about the files in the second-level directory in asynchronous mode. This method uses a promise to return the result.
+
+- Parameters
+  | Name| Type| Mandatory| Description|
+  | --- | --- | --- | -- |
+  | type | string | Yes| Type of the files to query. The file type can be **file**, **image**, **audio**, or **video**.|
+  | path | string | Yes| URI of the directory to query.|
+  | dev | [DevInfo](#devinfo) | Yes| Device name. The default value is **local**, which is the only value supported.|
+  | offset | number | No| Start position from which the files are to query.|
+  | count | number | No| Number of files to query.|
+
+- Return value
+
+  | Type| Description|
+  | --- | -- |
+  | Promise&lt;FileInfo[]&gt; | Promise used to return the file information obtained.|
+
+- Error
+  |  | Error Info| Error Code|Description|
+  | --- | -- | --- | -- |
+  |  | No such file or directory | 2      | The directory or file of the specified URI does not exist.|
+  |  | No such process | 3 | Failed to obtain the FMS service.|
+  |  | Not a directory | 20 | The object specified by the URI is not a directory.|
+
+```js
+// Obtain all files in the directory.
+// Call listFile() and getRoot() to obtain file URIs.
+let media_path = file.uri
+filemanager.listFile(media_path, "file")
+.then((fileInfo) => {
+    if(Array.isArray(fileInfo)) {
+        for (var i = 0; i < fileInfo.length; i++) {
+            console.log(JSON.Stringify(fileInfo))
+        }
+    }
+})
+.catch((err) => {
+    console.log(err)
+})
+```
+## filemanager.listFile
+
+listFile(path : string, type : string, options? : {dev? : DevInfo, offset? : number, count? : number}, callback : AsyncCallback&lt;FileInfo[]&gt;) : void
+
+Obtains information about the files in the second-level directory in asynchronous mode. This method uses a callback to return the result.
+
+- Parameters
+
+  | Name| Type| Mandatory| Description|
+  | -------- | ------------------------- | ---- | ------------------------------------------------------------ |
+  | type     | string                    | Yes| Type of the files to query. The file type can be **file**, **image**, **audio**, or **video**.|
+  | path     | string                    | Yes| URI of the directory to query.|
+  | dev | [DevInfo](#devinfo) | No| Device name. The default value is **local**, which is the only value supported.|
+  | offset | number | No| Start position from which the files are to query.|
+  | count | number | No| Number of files to query.|
+  | callback | AsyncCallback&lt;[FileInfo](#fileinfo)[]&gt; | Yes| Callback invoked to return the file information obtained.|
+- Error
+
+  |  | Error Info| Error Code| Description|
+  | ------------------------- | ------------------------- | ------ | ------------------------- |
+  |     | No such file or directory | 2      | The directory or file of the specified URI does not exist.|
+  |            | No such process           | 3      | Failed to obtain the FMS service.|
+  |  | Not a directory           | 20     | The object specified by the URI is not a directory.|
+
+```js
+// Call listFile() and getRoot() to obtain the file UIRs.
+let media_path = file.uri
+filemanager.listFile(media_path, "file", (err, fileInfo) => {
+    if(Array.isArray(fileInfo)) {
+        for (var i = 0; i < fileInfo.length; i++) {
+            console.log(JSON.Stringify(fileInfo))
+        }
+    }
+})
+```
+
+## filemanager.createFile
+
+filemanager.createFile(path : string, filename : string, options? : {dev? : DevInfo})  :   promise&lt;string&gt;
+
+Creates a file in the specified path in asynchronous mode. This method uses a promise to return the result.
+
+- Parameters
+  | Name| Type| Mandatory| Description|
+  | --- | --- | --- | -- |
+  | filename | string | Yes| Name of the file to create.|
+  | path | string | Yes| URI of the file to create.|
+  | dev | [DevInfo](#devinfo) | No| Device name. The default value is **local**, which is the only value supported.|
+
+- Return value
+
+  | Type| Description|
+  | --- | -- |
+  | promise<string>| Promise used to return the URI of the file created.|
+
+- Error
+  |  | Error Info| Error Code|Description|
+  | --- | -- | --- | -- |
+  |  | Operation not permitted | 1 | A file with the same name already exists.|
+  |  | No such file or directory | 2 | The directory or file of the specified URI does not exist.|
+  |  | No such process | 3 | Failed to obtain the FMS service.|
+  |  | Not a directory | 20 | The object specified by the URI is not a directory.|
+
+```js
+// Create a file.
+let media_path = file.uri // Obtain the file URI using listFile() and getRoot().
+let name = "xxx.jpg" // File name extension of the file to be saved.
+filemanager.createFile(media_path, name)
+.then((uri) => {
+// The URI of the file created is returned.
+})
+.catch((err) => {
+    console.log(err)
+})
+```
+
+## filemanager.createFile
+
+createFile(path : string, filename: string, options? : {dev? : DevInfo}, callback : AsyncCallback&lt;string&gt;) : void
+
+Creates a file in the specified path in asynchronous mode. This method uses a callback to return the result.
+
+- Parameters
+
+  | Name| Type| Mandatory| Description|
+  | -------- | ------------------------- | ---- | ----------------------------- |
+  | filename | string                    | Yes| Name of the file to create.|
+  | path     | string                    | Yes| URI of the file to create.|
+  | dev | [DevInfo](#devinfo) | No| Device name. The default value is **local**, which is the only value supported.|
+  | callback | AsyncCallback&lt;[FileInfo](#fileinfo)[]&gt; | Yes| Callback invoked to return the URI of the file created.|
+
+- Error
+
+  |  | Error Info| Error Code| Description|
+  | ------------------------- | ------------------------- | ------ | ------------------------- |
+  |             | Operation not permitted   | 1      | A file with the same name already exists.|
+  |     | No such file or directory | 2      | The directory or file of the specified URI does not exist.|
+  |            | No such process           | 3      | Failed to obtain the FMS service.|
+  |  | Not a directory           | 20     | The object specified by the URI is not a directory.|
+
+```js
+// Create a file.
+// Call listFile() and getRoot() to obtain the file URI.
+let media_path = file.uri
+// File name extension of file to be saved.
+let name = "xxx.jpg"
+filemanager.createFile(media_path, name, (err, uri) => {
+// The URI of the file created is returned.
+})
+```
+
+## FileInfo
+Defines the file information returned by **getRoot()** or **listFile()**.
+
+### Attributes
+
+| Name| Type| Readable| Writable| Description|
+| --- | -- | -- | -- | -- |
+| name | string | Yes| No| File name.|
+| path | string | Yes| No| URI of the file.|
+| type | string | Yes| No| File type.|
+| size | number | Yes| No| File size.|
+| addedTime | number | Yes| No| Time when the file was scanned to the database.|
+| modifiedTime | number | Yes| No| Time when the file was modified.|
+
+## DevInfo
+Defines the device type.
+
+### Attributes
+
+  | Name| Type| Readable| Writable| Description|
+  | --- | -- | -- | -- | -- |
+  | name | string | Yes| Yes| Device name.|