only print the 'no abort controller' warning if actually used

Author: isaacs

src/index.ts

@@ -37,22 +37,7 @@ let AC = globalThis.AbortController
 let AS = globalThis.AbortSignal
 
 /* c8 ignore start */
-if (
-  typeof AC === 'undefined' &&
-  PROCESS.env?.LRU_CACHE_IGNORE_AC_WARNING !== '1'
-) {
-  emitWarning(
-    'AbortController is not defined. If using lru-cache in ' +
-      'node 14, load an AbortController polyfill from the ' +
-      '`node-abort-controller` package. A minimal polyfill is ' +
-      'provided for use by LRUCache.fetch(), but it should not be ' +
-      'relied upon in other contexts (eg, passing it to other APIs that ' +
-      'use AbortController/AbortSignal might have undesirable effects). ' +
-      'You may disable this with LRU_CACHE_IGNORE_AC_WARNING=1 in the env.',
-    'NO_ABORT_CONTROLLER',
-    'ENOTSUP',
-    () => {}
-  )
+if (typeof AC === 'undefined') {
   //@ts-ignore
   AS = class AbortSignal {
     onabort?: (...a: any[]) => any
@@ -65,6 +50,9 @@ if (
   }
   //@ts-ignore
   AC = class AbortController {
+    constructor() {
+      warnACPolyfill()
+    }
     signal = new AS()
     abort(reason: any) {
       if (this.signal.aborted) return
@@ -79,6 +67,24 @@ if (
       this.signal.onabort?.(reason)
     }
   }
+  let printACPolyfillWarning =
+    PROCESS.env?.LRU_CACHE_IGNORE_AC_WARNING !== '1'
+  const warnACPolyfill = () => {
+    if (!printACPolyfillWarning) return
+    printACPolyfillWarning = false
+    emitWarning(
+      'AbortController is not defined. If using lru-cache in ' +
+        'node 14, load an AbortController polyfill from the ' +
+        '`node-abort-controller` package. A minimal polyfill is ' +
+        'provided for use by LRUCache.fetch(), but it should not be ' +
+        'relied upon in other contexts (eg, passing it to other APIs that ' +
+        'use AbortController/AbortSignal might have undesirable effects). ' +
+        'You may disable this with LRU_CACHE_IGNORE_AC_WARNING=1 in the env.',
+      'NO_ABORT_CONTROLLER',
+      'ENOTSUP',
+      warnACPolyfill
+    )
+  }
 }
 /* c8 ignore stop */
 

test/warn-missing-ac.ts

@@ -4,9 +4,10 @@ const main = async () => {
   const { spawn } = await import('child_process')
 
   // need to run both tests in parallel so we don't miss the close event
-  t.jobs = 2
+  t.jobs = 3
 
-  const tsNode = process.platform === 'win32' ? 'ts-node.cmd' : 'ts-node'
+  const tsNode =
+    process.platform === 'win32' ? 'ts-node.cmd' : 'ts-node'
 
   const warn = spawn(tsNode, [__filename, 'child'])
   const warnErr: Buffer[] = []
@@ -21,6 +22,10 @@ const main = async () => {
   const noWarnErr: Buffer[] = []
   noWarn.stderr.on('data', c => noWarnErr.push(c))
 
+  const noFetch = spawn(tsNode, [__filename, 'child-no-fetch'])
+  const noFetchErr: Buffer[] = []
+  noFetch.stderr.on('data', c => noFetchErr.push(c))
+
   t.test('no warning', async t => {
     await new Promise<void>(r =>
       noWarn.on('close', (code, signal) => {
@@ -32,6 +37,17 @@ const main = async () => {
     t.equal(Buffer.concat(noWarnErr).toString().trim(), '')
   })
 
+  t.test('no warning (because no fetch)', async t => {
+    await new Promise<void>(r =>
+      noFetch.on('close', (code, signal) => {
+        t.equal(code, 0)
+        t.equal(signal, null)
+        r()
+      })
+    )
+    t.equal(Buffer.concat(noFetchErr).toString().trim(), '')
+  })
+
   t.test('warning', async t => {
     await new Promise<void>(r =>
       warn.on('close', (code, signal) => {
@@ -46,6 +62,15 @@ const main = async () => {
 
 switch (process.argv[2]) {
   case 'child':
+    //@ts-ignore
+    globalThis.AbortController = undefined
+    //@ts-ignore
+    globalThis.AbortSignal = undefined
+    import('../').then(({ LRUCache }) => {
+      new LRUCache({ max: 1, fetchMethod: async () => 1 }).fetch(1)
+    })
+    break
+  case 'child-no-fetch':
     //@ts-ignore
     globalThis.AbortController = undefined
     //@ts-ignore