Test if a given function is promise

ispromise.js

// From graphql-js, https://github.com/graphql/graphql-js/blob/499a75939f70c4863d44149371d6a99d57ff7c35/src/jsutils/isPromise.js#L18
function isPromiseWithBoxing(value) {
  return Boolean(value && typeof value.then === "function");
}
// Tailor source -  https://github.com/zalando/tailor/blob/0d930d30d6ea3936985ecf3714a3d93fa755b628/src/pipe.js#L53
function isPromiseWithoutBoxing(value) {
  return (
    value != null &&
    typeof value === "object" &&
    typeof value.then === "function"
  );
}

function isPromiseWithoutBoxing2(value) {
  return value && typeof value.then === "function";
}

// From bluebird source - https://github.com/petkaantonov/bluebird/blob/3746b7eca90dd8b11af73db5d30cf46d7dd90f9b/test/mocha/helpers/bluebird0_7_0.js#L674
function isPromiseBluebird(obj) {
  if (typeof obj !== "object") return false;
  return obj instanceof Promise;
}

const dumbPromise1 = Promise.resolve(1);
const dumbPromise2 = Promise.resolve(2);
const dumbPromise3 = Promise.resolve(3);
const dumbPromise4 = Promise.resolve(4);

console.time("isPromiseWithBoxing");
for (let i = 0; i < 1e7; i++) {
  isPromiseWithBoxing(dumbPromise1);
}
console.timeEnd("isPromiseWithBoxing");

console.time("isPromiseWithoutBoxing");
for (let i = 0; i < 1e7; i++) {
  isPromiseWithoutBoxing(dumbPromise2);
}
console.timeEnd("isPromiseWithoutBoxing");

console.time("isPromiseWithoutBoxing2");
for (let i = 0; i < 1e7; i++) {
  isPromiseWithoutBoxing2(dumbPromise3);
}
console.timeEnd("isPromiseWithoutBoxing2");

console.time("isPromiseBluebird");
for (let i = 0; i < 1e7; i++) {
  isPromiseBluebird(dumbPromise4);
}
console.timeEnd("isPromiseBluebird");

isPromiseWithBoxing: 18.091ms
isPromiseWithoutBoxing: 13.936ms
isPromiseWithoutBoxing2: 16.886ms
isPromiseBluebird: 41.380ms

When i change it to rejection

const dumbPromise1 = Promise.reject(1).catch(_ => {});
const dumbPromise2 = Promise.reject(2).catch(_ => {});
const dumbPromise3 = Promise.reject(3).catch(_ => {});
const dumbPromise4 = Promise.reject(4).catch(_ => {});

Results

isPromiseWithBoxing: 19.332ms
isPromiseWithoutBoxing: 14.083ms
isPromiseWithoutBoxing2: 17.172ms
isPromiseBluebird: 38.480ms