Signed-off-by: wangdongqi <wangdongqi2@huawei.com>

 Changes to be committed:

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

@@ -367,6 +367,7 @@ on(type: 'progress', callback:(uploadedSize: number, totalSize: number) => vo
 **示例：**
   
   ```js
+  let uploadTask;
   uploadTask.on('progress', function callback(uploadedSize, totalSize) {
       console.info("upload totalSize:" + totalSize + "  uploadedSize:" + uploadedSize);
   }
@@ -400,6 +401,7 @@ on(type: 'headerReceive', callback:  (header: object) => void): void
 **示例：**
   
   ```js
+  let uploadTask;
   uploadTask.on('headerReceive', function callback(headers){   
       console.info("upOnHeader headers:" + JSON.stringify(headers));
   }
@@ -433,6 +435,7 @@ on(type: 'headerReceive', callback:  (header: object) => void): void
 **示例：**
   
   ```js
+  let uploadTask;
   uploadTask.on('complete', function callback(taskStates) {
     for (let i = 0; i < taskStates.length; i++ ) {
       console.info("upOnComplete taskState:" + JSON.stringify(taskStates[i]));
@@ -476,6 +479,7 @@ off(type:  'progress',  callback?: (uploadedSize: number, totalSize: number) =&g
 **示例：**
   
   ```js
+  let uploadTask;
   uploadTask.off('progress', function callback(uploadedSize, totalSize) {
       console.info('uploadedSize: ' + uploadedSize, 'totalSize: ' + totalSize);
   }
@@ -509,6 +513,11 @@ off(type: 'headerReceive', callback?: (header: object) =&gt; void): void
 **示例：**
   
   ```js
+  let uploadTask;
+  uploadTask.off('progress', function callback(uploadedSize, totalSize) {
+      console.info('uploadedSize: ' + uploadedSize, 'totalSize: ' + totalSize);
+  }
+  );
   uploadTask.off('headerReceive', function callback(headers) {
       console.info("upOnHeader headers:" + JSON.stringify(headers));
   }
@@ -541,6 +550,11 @@ off(type: 'headerReceive', callback?: (header: object) =&gt; void): void
 **示例：**
   
   ```js
+  let uploadTask;
+  uploadTask.off('progress', function callback(uploadedSize, totalSize) {
+      console.info('uploadedSize: ' + uploadedSize, 'totalSize: ' + totalSize);
+  }
+  );
   uploadTask.off('complete', function callback(taskStates) {
     for (let i = 0; i < taskStates.length; i++ ) {
       console.info("upOnComplete taskState:" + JSON.stringify(taskStates[i]));
@@ -578,6 +592,7 @@ remove(): Promise&lt;boolean&gt;
 **示例：**
   
   ```js
+  let uploadTask;
   uploadTask.remove().then((result) => {
       if (result) {
           console.info('Upload task removed successfully. ');
@@ -611,6 +626,7 @@ remove(callback: AsyncCallback&lt;boolean&gt;): void
 **示例：**
   
   ```js
+  let uploadTask;
   uploadTask.remove((err, result) => {
       if (err) {
           console.error('Failed to remove the upload task. Cause: ' + JSON.stringify(err));
@@ -644,6 +660,7 @@ delete(): Promise&lt;boolean&gt;
 **示例：**
 
   ```js
+  let uploadTask;
   uploadTask.delete().then((result) => {
       if (result) {
           console.info('Upload task removed successfully. ');
@@ -675,6 +692,7 @@ delete(callback: AsyncCallback&lt;boolean&gt;): void
 **示例：**
 
   ```js
+  let uploadTask;
   uploadTask.delete((err, result) => {
       if (err) {
           console.error('Failed to remove the upload task. Cause: ' + JSON.stringify(err));
@@ -1004,6 +1022,7 @@ on(type: 'progress', callback:(receivedSize: number, totalSize: number) =&gt; vo
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.on('progress', function download_callback(receivedSize, totalSize) {
       console.info("download receivedSize:" + receivedSize + " totalSize:" + totalSize);
   }
@@ -1065,6 +1084,7 @@ on(type: 'complete'|'pause'|'remove', callback:() =&gt; void): void
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.on('complete', function callback() {
       console.info('Download task completed.');
   }
@@ -1092,6 +1112,7 @@ off(type: 'complete'|'pause'|'remove', callback?:() =&gt; void): void
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.off('complete', function callback() {
       console.info('Download task completed.');
   }
@@ -1125,6 +1146,7 @@ on(type: 'fail', callback: (err: number) =&gt; void): void
 **示例：**
   
   ```js 
+  let downloadTask;
   downloadTask.on('fail', function callBack(err) {
       console.info('Download task failed. Cause:' + err);
   }
@@ -1158,6 +1180,7 @@ off(type: 'fail', callback?: (err: number) =&gt; void): void
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.off('fail', function callBack(err) {
       console.info('Download task failed. Cause:' + err);
   } 
@@ -1186,6 +1209,7 @@ remove(): Promise&lt;boolean&gt;
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.remove().then((result) => {
       if (result) {
           console.info('Download task removed.');
@@ -1219,6 +1243,7 @@ remove(callback: AsyncCallback&lt;boolean&gt;): void
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.remove((err, result)=>{
       if(err) {
           console.error('Failed to remove the download task.');
@@ -1253,6 +1278,7 @@ query(): Promise&lt;DownloadInfo&gt;
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.query().then((downloadInfo) => {    
       console.info('Download task queried. Data:' + JSON.stringify(downloadInfo))
   }) .catch((err) => {
@@ -1282,6 +1308,7 @@ query(callback: AsyncCallback&lt;DownloadInfo&gt;): void
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.query((err, downloadInfo)=>{
       if(err) {
           console.error('Failed to query the download mimeType. Cause:' + JSON.stringify(err));
@@ -1313,6 +1340,7 @@ queryMimeType(): Promise&lt;string&gt;
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.queryMimeType().then((data) => {    
       console.info('Download task queried. Data:' + JSON.stringify(data));
   }).catch((err) => {
@@ -1342,6 +1370,7 @@ queryMimeType(callback: AsyncCallback&lt;string&gt;): void;
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.queryMimeType((err, data)=>{
       if(err) {
           console.error('Failed to query the download mimeType. Cause:' + JSON.stringify(err));
@@ -1373,6 +1402,7 @@ pause(): Promise&lt;void&gt;
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.pause().then((result) => {    
       if (result) {
            console.info('Download task paused. ');
@@ -1406,6 +1436,7 @@ pause(callback: AsyncCallback&lt;void&gt;): void
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.pause((err, result)=>{
       if(err) {
           console.error('Failed to pause the download task. Cause:' + JSON.stringify(err));
@@ -1441,6 +1472,7 @@ resume(): Promise&lt;void&gt;
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.resume().then((result) => {
       if (result) {
           console.info('Download task resumed.')
@@ -1475,6 +1507,7 @@ resume(callback: AsyncCallback&lt;void&gt;): void
 **示例：**
   
   ```js
+  let downloadTask;
   downloadTask.resume((err, result)=>{
       if (err) {
           console.error('Failed to resume the download task. Cause:' + err);
@@ -1508,6 +1541,7 @@ delete(): Promise&lt;boolean&gt;
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.delete().then((result) => {
       if (result) {
           console.info('Download task removed.');
@@ -1539,6 +1573,7 @@ delete(callback: AsyncCallback&lt;boolean&gt;): void
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.delete((err, result)=>{
       if(err) {
           console.error('Failed to remove the download task.');
@@ -1571,6 +1606,7 @@ getTaskInfo(): Promise&lt;DownloadInfo&gt;
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.getTaskInfo().then((downloadInfo) => {    
       console.info('Download task queried. Data:' + JSON.stringify(downloadInfo))
   }) .catch((err) => {
@@ -1598,6 +1634,7 @@ query(callback: AsyncCallback&lt;DownloadInfo&gt;): void
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.getTaskInfo((err, downloadInfo)=>{
       if(err) {
           console.error('Failed to query the download mimeType. Cause:' + JSON.stringify(err));
@@ -1627,6 +1664,7 @@ getTaskMimeType(): Promise&lt;string&gt;
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.getTaskMimeType().then((data) => {    
       console.info('Download task queried. Data:' + JSON.stringify(data));
   }).catch((err) => {
@@ -1654,6 +1692,7 @@ getTaskMimeType(callback: AsyncCallback&lt;string&gt;): void;
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.getTaskMimeType((err, data)=>{
       if(err) {
           console.error('Failed to query the download mimeType. Cause:' + JSON.stringify(err));
@@ -1683,6 +1722,7 @@ suspend(): Promise&lt;void&gt;
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.suspend().then((result) => {    
       if (result) {
            console.info('Download task paused. ');
@@ -1714,6 +1754,7 @@ suspend(callback: AsyncCallback&lt;void&gt;): void
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.suspend((err, result)=>{
       if(err) {
           console.error('Failed to pause the download task. Cause:' + JSON.stringify(err));
@@ -1747,6 +1788,7 @@ restore(): Promise&lt;void&gt;
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.restore().then((result) => {
       if (result) {
           console.info('Download task resumed.')
@@ -1779,6 +1821,7 @@ restore(callback: AsyncCallback&lt;void&gt;): void
 **示例：**
 
   ```js
+  let downloadTask;
   downloadTask.restore((err, result)=>{
       if (err) {
           console.error('Failed to resume the download task. Cause:' + err);