Defer importing ky-universal until actually needed

lib/deferred.js

@@ -0,0 +1,16 @@
+export function deferred(f) {
+  let promise;
+
+  return {
+    then(
+      onfulfilled,
+      onrejected
+    ) {
+      promise ||= new Promise(resolve => resolve(f()));
+      return promise.then(
+        onfulfilled,
+        onrejected
+      );
+    },
+  };
+}

lib/httpClient.js

@@ -2,9 +2,10 @@
  * Copyright (c) 2020-2022 Digital Bazaar, Inc. All rights reserved.
  */
 import {convertAgent} from './agentCompatibility.js';
+import {deferred} from './deferred.js';
 
-export const kyOriginalPromise = import('ky-universal')
-  .then(({default: ky}) => ky);
+export const kyOriginalPromise = deferred(() => import('ky-universal')
+  .then(({default: ky}) => ky));
 
 export const DEFAULT_HEADERS = {
   Accept: 'application/ld+json, application/json'
@@ -33,7 +34,7 @@ export function createInstance({
   params = convertAgent(params);
 
   // create new ky instance that will asynchronously resolve
-  const kyPromise = parent.then(kyBase => {
+  const kyPromise = deferred(() => parent.then(kyBase => {
     let ky;
     if(parent === kyOriginalPromise) {
       // ensure default headers, allow overrides
@@ -46,7 +47,7 @@ export function createInstance({
       ky = kyBase.extend({headers, ...params});
     }
     return ky;
-  });
+  }));
 
   return _createHttpClient(kyPromise);
 }

tests/deferred.spec.js

@@ -0,0 +1,50 @@
+import {deferred} from '../lib/deferred.js';
+
+describe('deferred()', () => {
+  it('resolves to the return value of its function', async () => {
+    const d = deferred(() => {
+      return 'return value';
+    });
+
+    const ret = await d;
+    ret.should.equal('return value');
+  });
+
+  it('defers execution until awaited', async () => {
+    let executionCount = 0;
+    executionCount.should.equal(0);
+
+    const d = deferred(() => {
+      executionCount++;
+      return 'return value';
+    });
+
+    executionCount.should.equal(0);
+    await d;
+    executionCount.should.equal(1);
+  });
+
+  it('only executes once', async () => {
+    let executionCount = 0;
+    executionCount.should.equal(0);
+
+    const d = deferred(() => {
+      executionCount++;
+      return 'return value';
+    });
+
+    await d;
+    await d;
+    executionCount.should.equal(1);
+  });
+
+  it('unwraps returned promises', async () => {
+    const d = deferred(() => {
+      return Promise.resolve('return value');
+    });
+
+    const ret = await d;
+    ret.should.equal('return value');
+  });
+});
+