Update only if still available

1 files changed, 10 insertions, 8 deletions

diff --git a/src/rx.ts b/src/rx.ts
index 42680c5..61a7e7f 100644
--- a/src/rx.ts
+++ b/src/rx.ts
@@ -261,14 +261,16 @@ class State {
   }
 
   update<A>(v: Var<A>, f: (value: A) => A) {
-    const value = f(this.state[v.id].value)
-    this.state[v.id].value = value
-    this.state[v.id].subscribers.forEach(notify => {
-      // Don’t notify if it has been removed from a precedent notifier
-      if (this.state[v.id].subscribers.indexOf(notify) !== -1) {
-        notify(value)
-      }
-    })
+    if (v.id in this.state) {
+        const value = f(this.state[v.id].value)
+        this.state[v.id].value = value
+        this.state[v.id].subscribers.forEach(notify => {
+          // Don’t notify if it has been removed from a precedent notifier
+          if (this.state[v.id].subscribers.indexOf(notify) !== -1) {
+            notify(value)
+          }
+        })
+    }
   }
 
   subscribe<A>(v: Var<A>, notify: (value: A) => void): Cancelable {