get thumbnail from video js

1function getVideoCover(file, seekTo = 0.0) {
2    console.log("getting video cover for file: ", file);
3    return new Promise((resolve, reject) => {
4        // load the file to a video player
5        const videoPlayer = document.createElement('video');
6        videoPlayer.setAttribute('src', URL.createObjectURL(file));
7        videoPlayer.load();
8        videoPlayer.addEventListener('error', (ex) => {
9            reject("error when loading video file", ex);
10        });
11        // load metadata of the video to get video duration and dimensions
12        videoPlayer.addEventListener('loadedmetadata', () => {
13            // seek to user defined timestamp (in seconds) if possible
14            if (videoPlayer.duration < seekTo) {
15                reject("video is too short.");
16                return;
17            }
18            // delay seeking or else 'seeked' event won't fire on Safari
19            setTimeout(() => {
20              videoPlayer.currentTime = seekTo;
21            }, 200);
22            // extract video thumbnail once seeking is complete
23            videoPlayer.addEventListener('seeked', () => {
24                console.log('video is now paused at %ss.', seekTo);
25                // define a canvas to have the same dimension as the video
26                const canvas = document.createElement("canvas");
27                canvas.width = videoPlayer.videoWidth;
28                canvas.height = videoPlayer.videoHeight;
29                // draw the video frame to canvas
30                const ctx = canvas.getContext("2d");
31                ctx.drawImage(videoPlayer, 0, 0, canvas.width, canvas.height);
32                // return the canvas image as a blob
33                ctx.canvas.toBlob(
34                    blob => {
35                        resolve(blob);
36                    },
37                    "image/jpeg",
38                    0.75 /* quality */
39                );
40            });
41        });
42    });
43}
44