Enable "no-sequences" ESLint rule (#1883)

.eslintrc.yml

@@ -149,7 +149,7 @@ rules:
   no-script-url: error
   no-self-assign: error
   no-self-compare: off # TODO
-  no-sequences: off # TODO
+  no-sequences: error
   no-throw-literal: error
   no-unmodified-loop-condition: error
   no-unused-expressions: error

src/jsutils/keyMap.js

@@ -36,8 +36,8 @@ export default function keyMap<T>(
   list: $ReadOnlyArray<T>,
   keyFn: (item: T) => string,
 ): ObjMap<T> {
-  return list.reduce(
-    (map, item) => ((map[keyFn(item)] = item), map),
-    Object.create(null),
-  );
+  return list.reduce((map, item) => {
+    map[keyFn(item)] = item;
+    return map;
+  }, Object.create(null));
 }

src/jsutils/keyValMap.js

@@ -31,8 +31,8 @@ export default function keyValMap<T, V>(
   keyFn: (item: T) => string,
   valFn: (item: T) => V,
 ): ObjMap<V> {
-  return list.reduce(
-    (map, item) => ((map[keyFn(item)] = valFn(item)), map),
-    Object.create(null),
-  );
+  return list.reduce((map, item) => {
+    map[keyFn(item)] = valFn(item);
+    return map;
+  }, Object.create(null));
 }

src/type/schema.js

@@ -257,10 +257,10 @@ export class GraphQLSchema {
 
     if (!possibleTypeMap[abstractType.name]) {
       const possibleTypes = this.getPossibleTypes(abstractType);
-      possibleTypeMap[abstractType.name] = possibleTypes.reduce(
-        (map, type) => ((map[type.name] = true), map),
-        Object.create(null),
-      );
+      possibleTypeMap[abstractType.name] = possibleTypes.reduce((map, type) => {
+        map[type.name] = true;
+        return map;
+      }, Object.create(null));
     }
 
     return Boolean(possibleTypeMap[abstractType.name][possibleType.name]);