feat(env): Environment variables are now being cached, improving performance

Author: spuxx-dev

packages/nest-utils/src/env/env.module-mixin.test.ts

@@ -18,6 +18,20 @@ describe('registration', () => {
     expect(module).toBeDefined();
     expect(EnvModule.get('SOME_STRING')).toBe('foo');
   });
+
+  it('should cache environment variables until load() is called again', async () => {
+    vi.stubEnv('SOME_STRING', 'foo');
+    const container = await TestContainer.create({
+      imports: [EnvModule],
+    });
+    const module = container.module.get<EnvModule>(EnvModule);
+    expect(module).toBeDefined();
+    expect(EnvModule.get('SOME_STRING')).toBe('foo');
+    vi.stubEnv('SOME_STRING', 'bar');
+    expect(EnvModule.get('SOME_STRING')).toBe('foo');
+    EnvModule.load();
+    expect(EnvModule.get('SOME_STRING')).toBe('bar');
+  });
 });
 
 describe('validation', () => {

packages/nest-utils/src/env/env.module-mixin.ts

@@ -34,17 +34,25 @@ import { config } from 'dotenv';
 export function EnvModuleMixin<TEnv extends object>(env: new (...args: unknown[]) => TEnv) {
   @Module({})
   class EnvModule {
-    static get env(): TEnv {
-      config();
-      return plainToInstance(env, process.env, {
-        enableImplicitConversion: true,
-      });
-    }
+    static readonly env: TEnv;
 
     constructor() {
+      EnvModule.load();
       EnvModule.validate();
     }
 
+    /**
+     * (Re-)loads the environment variables. This comes at a performance cost and should only be used
+     * when necessary.
+     */
+    static load(): void {
+      config();
+      // @ts-expect-error This is the only spot where we're allowed to write to this.env.
+      this.env = plainToInstance(env, process.env, {
+        enableImplicitConversion: true,
+      });
+    }
+
     /**
      * Validates the currently stored instance of the environment class.
      */
@@ -68,7 +76,7 @@ export function EnvModuleMixin<TEnv extends object>(env: new (...args: unknown[]
      * @returns The value of the environment variable.
      */
     static get<TKey extends keyof TEnv>(key: TKey): TEnv[TKey] {
-      return EnvModule.env[key];
+      return this.env[key];
     }
   }