update docs

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

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

+# statfs
+
+
+
+## Modules to Import
+
+```
+import statfs from '@ohos.statfs'
+```
+
+## Note
+
+Before using this module to perform operations on a file or directory, obtain the absolute path of the file or directory. For details, see [getOrCreateLocalDir of the Context module](js-apis-Context.md).
+
+Absolute file or directory path = Application directory + File name or directory name
+
+For example, if the application directory obtained by using **getOrCreateLocalDir** is **dir** and the file name is **xxx.txt**, the absolute path of the file is as follows:
+
+```
+let path = dir + "xxx.txt"
+```
+
+## Required Permissions
+
+None
+
+## statfs.getFreeBytes
+
+getFreeBytes(path:string):Promise<number>
+
+Obtains the number of free bytes of the specified file system in asynchronous mode. This method uses a promise to return the result.
+
+- Parameters
+
+  | Name| Type| Mandatory| Description|
+  | ------ | ------ | ---- | ---------------------------- |
+  | path   | string | Yes| File path of the file system.|
+
+- Return values
+
+  | Type| Description|
+  | --------------------- | -------------- |
+  | Promise<number> | Number of free bytes obtained.|
+
+- Example
+
+  ```
+  let num = await statfs.getFreeBytes(path);
+  ```
+
+## statfs.getFreeBytes
+
+getFreeBytes(path:string, callback:AsyncCallback<number>): void
+
+Obtains the number of free bytes of the specified file system in asynchronous mode. This method uses a callback to return the result.
+
+- Parameters
+
+  | Name| Type| Mandatory| Description|
+  | -------- | --------------------------- | ---- | ---------------------------- |
+  | path     | string                      | Yes| File path of the file system.|
+  | callback | AsyncCallback<number> | Yes| Callback invoked to return the number of free bytes obtained.|
+
+- Example
+
+  ```
+  statfs.getFreeBytes(path, function(err, number){
+      //do something
+  });
+  ```
+
+## statfs.getTotalBytes
+
+getTotalBytes.(path:string):Promise<number>
+
+Obtains the total number of bytes of the specified file system in asynchronous mode. This method uses a promise to return the result.
+
+- Parameters
+
+  | Name| Type| Mandatory| Description|
+  | ---- | ------ | ---- | ---------------------------- |
+  | path | string | Yes| File path of the file system.|
+
+- Return values
+
+  | Type| Description|
+  | --------------------- | ------------ |
+  | Promise<number> | Total number of bytes obtained.|
+
+- Example
+
+  ```
+  let num = await statfs.getTotalBytes(path);
+  ```
+
+## statfs.getTotalBytes
+
+getTotalBytes(path:string, callback:AsyncCallback<number>): void
+
+Obtains the total number of bytes of the specified file system in asynchronous mode. This method uses a callback to return the result.
+
+- Parameters
+
+  | Name| Type| Mandatory| Description|
+  | -------- | --------------------------- | ---- | ---------------------------- |
+  | path     | string                      | Yes| File path of the file system.|
+  | callback | AsyncCallback<number> | Yes| Callback invoked to return the total number of bytes obtained.|
+
+- Example
+
+  ```
+  statfs.getTotalBytes(path, function(err, number){
+      //do something
+  });
+  ```