perf: partially replace .concat with .push (#13609)

packages/babel-types/src/comments/addComments.ts

@@ -16,7 +16,7 @@ export default function addComments<T extends t.Node>(
     if (type === "leading") {
       node[key] = comments.concat(node[key]);
     } else {
-      node[key] = node[key].concat(comments);
+      node[key].push(...comments);
     }
   } else {
     node[key] = comments;

packages/babel-types/src/modifications/flow/removeTypeDuplicates.ts

@@ -17,13 +17,14 @@ function getQualifiedName(node: t.GenericTypeAnnotation["id"]) {
  * Dedupe type annotations.
  */
 export default function removeTypeDuplicates(
+  // todo(babel-8): change type to Array<...>
   nodes: ReadonlyArray<t.FlowType | false | null | undefined>,
 ): t.FlowType[] {
   const generics = {};
   const bases = {};
 
   // store union type groups to circular references
-  const typeGroups = [];
+  const typeGroups = new Set<t.FlowType[]>();
 
   const types = [];
 
@@ -47,9 +48,10 @@ export default function removeTypeDuplicates(
     }
 
     if (isUnionTypeAnnotation(node)) {
-      if (typeGroups.indexOf(node.types) < 0) {
+      if (!typeGroups.has(node.types)) {
+        // todo(babel-8): use .push when nodes is mutable
         nodes = nodes.concat(node.types);
-        typeGroups.push(node.types);
+        typeGroups.add(node.types);
       }
       continue;
     }

packages/babel-types/src/modifications/typescript/removeTypeDuplicates.ts

@@ -15,7 +15,7 @@ export default function removeTypeDuplicates(
   const bases = {};
 
   // store union type groups to circular references
-  const typeGroups = [];
+  const typeGroups = new Set<t.TSType[]>();
 
   const types = [];
 
@@ -40,9 +40,9 @@ export default function removeTypeDuplicates(
     }
 
     if (isTSUnionType(node)) {
-      if (typeGroups.indexOf(node.types) < 0) {
-        nodes = nodes.concat(node.types);
-        typeGroups.push(node.types);
+      if (!typeGroups.has(node.types)) {
+        nodes.push(...node.types);
+        typeGroups.add(node.types);
       }
       continue;
     }