Convert simple class to function+object

src/fast-string-array.ts

@@ -1,3 +1,8 @@
+export interface FastStringArray {
+  indexes: { [key: string]: number };
+  array: readonly string[];
+}
+
 /**
  * FastStringArray acts like a `Set` (allowing only one occurrence of a string
  * `key`), but provides the index of the `key` in the backing array.
@@ -6,9 +11,11 @@
  * the backing array, like how `sourcesContent[i]` is the source content
  * associated with `source[i]`, and there are never duplicates.
  */
-export class FastStringArray {
-  indexes = Object.create(null) as { [key: string]: number };
-  array = [] as ReadonlyArray<string>;
+export function FastStringArray(): FastStringArray {
+  return {
+    indexes: { __proto__: null } as any,
+    array: [],
+  };
 }
 
 /**
@@ -29,4 +36,3 @@ export function put(strarr: FastStringArray, key: string): number {
 
   return index;
 }
-

src/source-map-tree.ts

@@ -17,8 +17,8 @@ type MappingSource = SourceMapSegmentObject | typeof INVALID_MAPPING | typeof SO
  */
 export function traceMappings(tree: SourceMapTree): TraceMap {
   const mappings: SourceMapSegment[][] = [];
-  const names = new FastStringArray();
-  const sources = new FastStringArray();
+  const names = FastStringArray();
+  const sources = FastStringArray();
   const sourcesContent: (string | null)[] = [];
   const { sources: rootSources, map } = tree;
   const rootNames = map.names;

test/unit/fast-array-string.ts

@@ -1,14 +1,10 @@
 import { FastStringArray, put } from '../../src/fast-string-array';
 
 describe('FastStringArray', () => {
-  let array: FastStringArray;
-
-  beforeEach(() => {
-    array = new FastStringArray();
-  });
-
   describe('put()', () => {
     test('puts string in if not present', () => {
+      const array = FastStringArray();
+
       put(array, 'test');
       expect(array.array).toEqual(['test']);
       put(array, 'test');
@@ -26,12 +22,16 @@ describe('FastStringArray', () => {
     });
 
     test('returns index of string in array', () => {
+      const array = FastStringArray();
+
       expect(put(array, 'test')).toBe(0);
       expect(put(array, 'foo')).toBe(1);
       expect(put(array, 'bar')).toBe(2);
     });
 
     test('returns original index of string in array', () => {
+      const array = FastStringArray();
+
       put(array, 'test');
       put(array, 'foo');
       put(array, 'bar');
@@ -42,6 +42,8 @@ describe('FastStringArray', () => {
     });
 
     test('handles empty string', () => {
+      const array = FastStringArray();
+
       expect(put(array, '')).toBe(0);
       expect(put(array, '')).toBe(0);
       expect(array.array).toEqual(['']);