optimizing ndjson file

src/app/modules/core/utils/ndjson.ts

@@ -19,7 +19,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */
-import { from, Observable, Observer, Subject } from 'rxjs';
+import { from, Observable, Observer} from 'rxjs';
 import { concatMap, filter, map, scan } from 'rxjs/operators';
 
 /*
@@ -37,15 +37,13 @@ export function stream(url: string): Observable<string> {
   const textStream = extractStream(xhr);
   const jsonStream = collate(textStream).pipe(
     concatMap((lineArray: string) => from(lineArray)),
-    map((x: string, _) => JSON.parse(x)),
+    map((x: string) => JSON.parse(x)),
   );
 
-  if (options.beforeOpen) {
-    options.beforeOpen(xhr);
-  }
+  options.beforeOpen?.(xhr);
 
-  xhr.open(options.method ? options.method : 'GET', url);
-  xhr.send(options.postData ? options.postData : null);
+  xhr.open(options.method ?? 'GET', url);
+  xhr.send(options.postData ?? null);
 
   return jsonStream;
 }
@@ -85,16 +83,18 @@ function collate(chunkStream: Observable<string>): Observable<string> {
  * flag "endWithNewline: true" which adds a trailing newline if one did not
  * exist in the source.
  */
-function extractStream(xhr: XMLHttpRequest): Observable<string> {
-  const options = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {};
+interface ExtractStreamOptions {
+  endWithNewline?: boolean;
+}
+function extractStream(xhr: XMLHttpRequest, options: ExtractStreamOptions = {}): Observable<string> {
   return new Observable((observer: Observer<string>) => {
     let charactersSeen = 0;
     const notified = () => {
-      if (xhr.readyState >= 3 && xhr.responseText.length > charactersSeen) {
+      if (xhr.readyState >= XMLHttpRequest.LOADING && xhr.responseText.length > charactersSeen) {
           observer.next(xhr.responseText.substring(charactersSeen));
           charactersSeen = xhr.responseText.length;
       }
-      if (xhr.readyState === 4) {
+      if (xhr.readyState === XMLHttpRequest.DONE) {
         if (options.endWithNewline && xhr.responseText[xhr.responseText.length - 1] !== '\n') {
           observer.next('\n');
         }
@@ -103,8 +103,6 @@ function extractStream(xhr: XMLHttpRequest): Observable<string> {
     };
     xhr.onreadystatechange = notified;
     xhr.onprogress = notified;
-    xhr.onerror = event => {
-      observer.error(event);
-    };
+    xhr.onerror = (event: ProgressEvent) => observer.error(event);
   });
 }