Add interface of ability

Signed-off-by: Nyuyaozhi <yuyaozhi@huawei.com>

zh-cn/application-dev/reference/apis/js-apis-Context.md

@@ -929,6 +929,53 @@ import featureAbility from '@ohos.ability.featureAbility'
 var context = featureAbility.getContext().getApplicationContext();
 ```
 
+## Context.getExternalCacheDir
+
+getExternalCacheDir(callback: AsyncCallback\<string>): void
+
+获取应用程序的外部缓存目录（callback形式）。
+
+**系统能力**：SystemCapability.Ability.AbilityRuntime.Core
+
+**参数：**
+
+| 名称       | 类型                     | 必填   | 描述                 |
+| -------- | ---------------------- | ---- | ------------------ |
+| callback | AsyncCallback\<string> | 是    | 返回应用程序的缓存目录的绝对路径。 |
+
+**示例：**
+
+```js
+import featureAbility from '@ohos.ability.featureAbility'
+var context = featureAbility.getContext();
+context.getExternalCacheDir()
+```
+
+## Context.getExternalCacheDir
+
+getExternalCacheDir(): Promise\<string>;
+
+获取应用程序的外部缓存目录（Promise形式）。
+
+**系统能力**：SystemCapability.Ability.AbilityRuntime.Core
+
+**返回值：**
+
+| 类型               | 说明               |
+| ---------------- | ---------------- |
+| Promise\<string> | 返回应用程序的缓存目录的绝对路径。 |
+
+**示例：**
+
+```js
+import featureAbility from '@ohos.ability.featureAbility'
+var context = featureAbility.getContext();
+context.getExternalCacheDir().then((data) => {
+    console.info("=======================>getExternalCacheDirCallback====================>");
+    console.info("====>data====>" + JSON.stringify(data));
+});
+```
+
 ## PermissionOptions
 
 **系统能力**：SystemCapability.Ability.AbilityRuntime.Core