nite · March 4, 2021 11:51 · Mar 4, 2021
diff --git a/toObservable.ts b/toObservable.ts
@@ -0,0 +1,34 @@
+import { Observable } from 'rxjs';
+import { computed, IValueDidChange } from 'mobx';
+import isNil from 'lodash/isNil';
+import omit from 'lodash/omit';
+import { IEqualsComparer } from 'mobx/lib/internal';
+
+interface ToObservableOptions<T> {
+    initial?: boolean;
+    equals?: IEqualsComparer<T>;
+}
+
+/***
+ * wrap function in mobx computed() and convert to observable
+ *
+ * @param observable - mobx observable property
+ * @param options - initial: whether to fire an initial event if the property is non-empty
+ */
+export function toObservable<T>(observable: () => T, options?: ToObservableOptions<T>): Observable<IValueDidChange<T>> {
+    const optionsToUse: ToObservableOptions<T> = { initial: true, ...options };
+    return new Observable((observer) => {
+        const fireInitial = isNil(optionsToUse.initial) || optionsToUse.initial;
+        const item = fireInitial && observable();
+        if (item) {
+            observer.next({
+                newValue: item,
+                object: item,
+                type: 'update',
+                oldValue: undefined,
+            });
+        }
+        computed(observable, omit(optionsToUse, ['initial'])).observe((item) => observer.next(item));
+    });
+}
+
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