Make it possible to store other non-numeric keys as well, while we ar…

…e at it.

src/types/observablearray.ts

@@ -96,21 +96,17 @@ const arrayTraps = {
     set(target, name, value): boolean {
         if (name === "length") {
             target[$mobx].setArrayLength(value)
-            return true
         }
         if (typeof name === "number") {
             arrayExtensions.set.call(target, name, value)
-            return true
         }
-        if (typeof name === "symbol") {
+        if (typeof name === "symbol" || isNaN(name)) {
             target[name] = value
-            return true
-        }
-        if (!isNaN(name)) {
+        } else {
+            // numeric string
             arrayExtensions.set.call(target, parseInt(name), value)
-            return true
         }
-        return false
+        return true
     },
     preventExtensions(target) {
         fail(`Observable arrays cannot be frozen`)

test/base/array.js

@@ -520,3 +520,25 @@ test("#2044 symbol key on array", () => {
     expect(reacted).toBe(false)
     d()
 })
+
+test("#2044 non-symbol key on array", () => {
+    const x = observable([1, 2])
+    const s = "test"
+    x[s] = 3
+    expect(x[s]).toBe(3)
+
+    let reacted = false
+    const d = reaction(
+        () => x[s],
+        () => {
+            reacted = true
+        }
+    )
+
+    x[s] = 4
+    expect(x[s]).toBe(4)
+
+    // although x[s] can be stored, it won't be reactive!
+    expect(reacted).toBe(false)
+    d()
+})