util: add internal createDeferredPromise()

The pattern of resolving/rejecting a Promise from outside of its
executor happens numerous times throughout the codebase (more than
what is updated here in fact). This commit abstracts that logic
into an internal utility function.

Author: cjihrig

lib/child_process.js

@@ -37,7 +37,6 @@ const {
   ObjectAssign,
   ObjectDefineProperty,
   ObjectPrototypeHasOwnProperty,
-  Promise,
   RegExpPrototypeTest,
   SafeSet,
   StringPrototypeSlice,
@@ -47,6 +46,7 @@ const {
 const {
   promisify,
   convertToValidSignal,
+  createDeferredPromise,
   getSystemErrorName
 } = require('internal/util');
 const { isArrayBufferView } = require('internal/util/types');
@@ -184,12 +184,7 @@ function exec(command, options, callback) {
 
 const customPromiseExecFunction = (orig) => {
   return (...args) => {
-    let resolve;
-    let reject;
-    const promise = new Promise((res, rej) => {
-      resolve = res;
-      reject = rej;
-    });
+    const { promise, resolve, reject } = createDeferredPromise();
 
     promise.child = orig(...args, (err, stdout, stderr) => {
       if (err !== null) {

lib/internal/blob.js

@@ -3,7 +3,6 @@
 const {
   ArrayFrom,
   ObjectSetPrototypeOf,
-  Promise,
   PromiseResolve,
   RegExpPrototypeTest,
   StringPrototypeToLowerCase,
@@ -29,6 +28,7 @@ const {
 } = require('internal/util/types');
 
 const {
+  createDeferredPromise,
   customInspectSymbol: kInspect,
   emitExperimentalWarning,
 } = require('internal/util');
@@ -56,15 +56,6 @@ const kLength = Symbol('kLength');
 
 let Buffer;
 
-function deferred() {
-  let res, rej;
-  const promise = new Promise((resolve, reject) => {
-    res = resolve;
-    rej = reject;
-  });
-  return { promise, resolve: res, reject: rej };
-}
-
 function lazyBuffer() {
   if (Buffer === undefined)
     Buffer = require('buffer').Buffer;
@@ -210,7 +201,7 @@ class Blob extends JSTransferable {
       promise,
       resolve,
       reject
-    } = deferred();
+    } = createDeferredPromise();
     job.ondone = (err, ab) => {
       if (err !== undefined)
         return reject(new AbortError());

lib/internal/util.js

@@ -420,11 +420,23 @@ function sleep(msec) {
   _sleep(msec);
 }
 
+function createDeferredPromise() {
+  let resolve;
+  let reject;
+  const promise = new Promise((res, rej) => {
+    resolve = res;
+    reject = rej;
+  });
+
+  return { promise, resolve, reject };
+}
+
 module.exports = {
   assertCrypto,
   cachedResult,
   convertToValidSignal,
   createClassWrapper,
+  createDeferredPromise,
   decorateErrorStack,
   deprecate,
   emitExperimentalWarning,