update docs against 8465

Signed-off-by: Nwusongqing <wusongqing@huawei.com>

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

@@ -60,7 +60,7 @@ Creates a **VideoPlayer** instance in asynchronous mode. This API uses a callbac
 let videoPlayer
 
 media.createVideoPlayer((error, video) => {
-   if (typeof(video) != 'undefined') {
+   if (video != null) {
        videoPlayer = video;
        console.info('video createVideoPlayer success');
    } else {
@@ -89,7 +89,7 @@ Creates a **VideoPlayer** instance in asynchronous mode. This API uses a promise
 let videoPlayer
 
 media.createVideoPlayer().then((video) => {
-   if (typeof(video) != 'undefined') {
+   if (video != null) {
        videoPlayer = video;
        console.info('video createVideoPlayer success');
    } else {
@@ -307,7 +307,7 @@ Seeks to the specified playback position.
 
 ```js
 audioPlayer.on('timeUpdate', (seekDoneTime) => {    // Set the 'timeUpdate' event callback.
-    if (typeof (seekDoneTime) == 'undefined') {
+    if (seekDoneTime == null) {
         console.info('audio seek fail');
         return;
     }
@@ -380,7 +380,7 @@ function printfDescription(obj) {
 }
 
 audioPlayer.getTrackDescription((error, arrlist) => {
-    if (typeof (arrlist) != 'undefined') {
+    if (arrlist != null) {
         for (let i = 0; i < arrlist.length; i++) {
             printfDescription(arrlist[i]);
         }
@@ -416,7 +416,7 @@ function printfDescription(obj) {
 }
 
 audioPlayer.getTrackDescription().then((arrlist) => {
-    if (typeof (arrlist) != 'undefined') {
+    if (arrlist != null) {
         arrayDescription = arrlist;
     } else {
         console.log('audio getTrackDescription fail');
@@ -491,7 +491,7 @@ audioPlayer.on('reset', () => {               // Set the 'reset' event callback.
     audioPlayer = undefined;
 });
 audioPlayer.on('timeUpdate', (seekDoneTime) => {  // Set the 'timeUpdate' event callback.
-    if (typeof(seekDoneTime) == "undefined") {
+    if (seekDoneTime == null) {
         console.info('audio seek fail');
         return;
     }
@@ -546,7 +546,7 @@ Subscribes to the 'timeUpdate' event.
 
 ```js
 audioPlayer.on('timeUpdate', (seekDoneTime) => {    // Set the 'timeUpdate' event callback.
-    if (typeof (seekDoneTime) == 'undefined') {
+    if (seekDoneTime == null) {
         console.info('audio seek fail');
         return;
     }
@@ -595,7 +595,6 @@ Enumerates the audio playback states. You can obtain the state through the **sta
 | stopped            | string | Audio playback is stopped.     |
 | error<sup>8+</sup> | string | Audio playback is in the error state.                                    |
 
-
 ## VideoPlayer<sup>8+</sup>
 
 Provides APIs to manage and play video. Before calling an API of **VideoPlayer**, you must call [createVideoPlayer()](#mediacreatevideoplayer8) to create a [VideoPlayer](#videoplayer8) instance.
@@ -635,7 +634,7 @@ Sets **SurfaceId**. This API uses a callback to return the result.
 
 ```js
 videoPlayer.setDisplaySurface(surfaceId, (err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('setDisplaySurface success!');
     } else {
         console.info('setDisplaySurface fail!');
@@ -691,7 +690,7 @@ Prepares for video playback. This API uses a callback to return the result.
 
 ```js
 videoPlayer.prepare((err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('prepare success!');
     } else {
         console.info('prepare fail!');
@@ -741,7 +740,7 @@ Starts to play video resources. This API uses a callback to return the result.
 
 ```js
 videoPlayer.play((err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('play success!');
     } else {
         console.info('play fail!');
@@ -791,7 +790,7 @@ Pauses video playback. This API uses a callback to return the result.
 
 ```js
 videoPlayer.pause((err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('pause success!');
     } else {
         console.info('pause fail!');
@@ -841,7 +840,7 @@ Stops video playback. This API uses a callback to return the result.
 
 ```js
 videoPlayer.stop((err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('stop success!');
     } else {
         console.info('stop fail!');
@@ -891,7 +890,7 @@ Switches the video resource to be played. This API uses a callback to return the
 
 ```js
 videoPlayer.reset((err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('reset success!');
     } else {
         console.info('reset fail!');
@@ -942,7 +941,7 @@ Seeks to the specified playback position. The next key frame at the specified po
 
 ```js
 videoPlayer.seek((seekTime, err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('seek success!');
     } else {
         console.info('seek fail!');
@@ -970,7 +969,7 @@ Seeks to the specified playback position. This API uses a callback to return the
 
 ```js
 videoPlayer.seek((seekTime, seekMode, err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('seek success!');
     } else {
         console.info('seek fail!');
@@ -1034,7 +1033,7 @@ Sets the volume. This API uses a callback to return the result.
 
 ```js
 videoPlayer.setVolume((vol, err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('setVolume success!');
     } else {
         console.info('setVolume fail!');
@@ -1090,7 +1089,7 @@ Releases the video playback resource. This API uses a callback to return the res
 
 ```js
 videoPlayer.release((err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('release success!');
     } else {
         console.info('release fail!');
@@ -1148,7 +1147,7 @@ function printfDescription(obj) {
 }
 
 videoPlayer.getTrackDescription((error, arrlist) => {
-    if (typeof (arrlist) != 'undefined') {
+    if (arrlist != null) {
         for (let i = 0; i < arrlist.length; i++) {
             printfDescription(arrlist[i]);
         }
@@ -1185,7 +1184,7 @@ function printfDescription(obj) {
 
 let arrayDescription;
 videoPlayer.getTrackDescription().then((arrlist) => {
-    if (typeof (arrlist) != 'undefined') {
+    if (arrlist != null) {
         arrayDescription = arrlist;
     } else {
         console.log('video getTrackDescription fail');
@@ -1217,7 +1216,7 @@ Sets the video playback speed. This API uses a callback to return the result.
 
 ```js
 videoPlayer.setSpeed((speed:number, err) => {
-    if (typeof (err) == 'undefined') {
+    if (err == null) {
         console.info('setSpeed success!');
     } else {
         console.info('setSpeed fail!');
@@ -1438,7 +1437,7 @@ function printfItemDescription(obj, key) {
 }
 
 audioPlayer.getTrackDescription((error, arrlist) => {
-    if (typeof (arrlist) != 'undefined') {
+    if (arrlist != null) {
         for (let i = 0; i < arrlist.length; i++) {
             printfItemDescription(arrlist[i], MD_KEY_TRACK_TYPE);  // Print the MD_KEY_TRACK_TYPE value of each track.
         }