diff --git a/README.md b/README.md
index b1eca20..d27c68f 100644
--- a/README.md
+++ b/README.md
@@ -5,49 +5,135 @@
 # Usage
 
 ```javascript
-const { ObjectPool } = require("@jacekpietal/object-pool");
-
-const pool = new ObjectPool(factory);
+const ObjectPool = require("@jacekpietal/object-pool");
+```
 
-// you should provide this function
-function factory() {
-  // that returns a new object instance
-}
+```javascript
+const pool = new ObjectPool(
+  // you should provide this function
+  function factory() {
+    // that returns a new object instance
+    // can be async
+  }
+);
 
 // will return value from pool
 // if pool empty uses factory function
-const nextValue = pool.next();
+const object = pool.get();
 
 // returns value to the pool
-pool.back(nextValue);
+pool.put(object);
+
+// prints 1
+console.log(pool.size);
+
+// removes value from pool
+pool.delete(object);
+
+// prints 0
+console.log(pool.size);
+
+// pre-fills pool up to size
+// useful I think only for async functions
+pool.size = 100;
+
+// empties pool
+pool.size = 0;
+
+// size manipulations do trigger as required
+// `put` and `delete` events for each change
+```
+
+## With Promises / async functions
+
+If you want to use async functions be sure to put the same thing you get from the pool.
+
+```javascript
+const pool = new ObjectPool(async () => "value");
+
+async function test() {
+  const once = pool.get();
+  const value1 = await once;
+
+  // put back the promise reference
+  pool.put(once);
+
+  const again = pool.get();
+  const value2 = await again;
+
+  // prints:
+  // {
+  //  once: Promise { 'value' },
+  //  again: Promise { 'value' },
+  //  value1: 'value',
+  //  value2: 'value'
+  // }
+  console.log({ once, again, value1, value2 });
+}
+
+test();
 ```
 
 # Events
 
 ```javascript
-pool.events.on("next", (value) => {
-  console.log({ next: value });
+// all actions are accompanied by EventEmitter events
+
+pool.events.on("get", (value) => {
+  console.log({ get: value });
 });
 
-pool.events.on("back", (value) => {
-  console.log({ back: value });
+pool.events.on("put", (value) => {
+  console.log({ put: value });
 });
 
-pool.events.on("remove", (value) => {
-  console.log({ remove: value });
+pool.events.on("delete", (value) => {
+  console.log({ delete: value });
 });
 ```
 
 # API
 
 ```javascript
-pool.next(); // returns next value from pool
+pool.get(); // returns get value from pool
 
-pool.back(object); // puts back value to end of pool
+pool.put(object); // puts put value to end of pool
 
-pool.empty(); // empties the whole pool
+pool.delete(object); // deletes object from pool manually
+```
 
-pool.remove(object); // removes object from pool manually
+# Tests
+
+Please check tests for more complicated cases:
+
+```bash
+$ yarn test
+yarn run v1.22.5
+$ jest
+ PASS  ./index.spec.js
+  GIVEN ObjectPool instance
+    ✓ THEN It should create (2 ms)
+    WHEN pool.get is called
+      ✓ THEN even if pool.size is 0 (1 ms)
+      ✓ THEN It should return new instance of factory call
+      ✓ THEN events.get should be emitted (1 ms)
+    WHEN pool.put is called
+      ✓ THEN pool.size should be greater than 0 afterwards
+      ✓ THEN events.put should be emitted (1 ms)
+    WHEN promise is `put` and then `get` again
+      ✓ THEN it still works as expected (1502 ms)
+    WHEN pool.size is set to 0 on non-empty pool
+      ✓ THEN events.delete should be emitted for each item (1 ms)
+    WHEN pool.size is set
+      ✓ THEN pool size adjusts and is being filled accordingly (2 ms)
+      ✓ THEN pool size adjusts and is being trimmed accordingly (1 ms)
+
+Test Suites: 1 passed, 1 total
+Tests:       10 passed, 10 total
+Snapshots:   0 total
+Time:        2.668 s
+Ran all test suites.
+Done in 3.41s.
 ```
 
 # License
diff --git a/index.js b/index.js
index 16de02f..29c5f61 100644
--- a/index.js
+++ b/index.js
@@ -3,53 +3,71 @@
 const EventEmitter = require("events");
 
 class ObjectPool {
-  constructor(factory) {
-    this.factory = factory;
+  constructor(factoryFunction) {
+    this.factory = factoryFunction;
+
     this.objects = new Set();
+
     this.events = new EventEmitter();
   }
 
-  empty() {
-    if (this.objects.size === 0) {
-      return;
+  get size() {
+    return this.objects.size;
+  }
+
+  set size(size = 0) {
+    if (typeof size !== "number") {
+      throw new Error("Parameter is not a number: " + typeof size);
     }
 
-    const [result] = this.objects.values();
+    let current = this.objects.size;
 
-    this.remove(result);
+    while (current < size) {
+      const object = this.factory();
 
-    this.empty();
-  }
+      this.put(object);
+
+      current++;
+    }
 
-  next() {
-    if (this.objects.size === 0) {
-      const result = this.factory();
+    while (current > size) {
+      const [object] = this.objects.values();
 
-      this.events.emit("next", result);
+      this.delete(object);
 
-      return result;
+      current--;
     }
+  }
 
-    const [result] = this.objects.values();
+  get() {
+    if (this.size === 0) {
+      const object = this.factory();
 
-    this.objects.delete(result);
+      this.events.emit("get", object);
 
-    this.events.emit("next", result);
+      return object;
+    }
 
-    return result;
-  }
+    const [object] = this.objects.values();
 
-  remove(object) {
     this.objects.delete(object);
 
-    this.events.emit("remove", object);
+    this.events.emit("get", object);
+
+    return object;
   }
 
-  back(object) {
+  put(object) {
     this.objects.add(object);
 
-    this.events.emit("back", object);
+    this.events.emit("put", object);
+  }
+
+  delete(object) {
+    this.objects.delete(object);
+
+    this.events.emit("delete", object);
   }
 }
 
-module.exports.ObjectPool = ObjectPool;
+module.exports = ObjectPool;
diff --git a/index.spec.js b/index.spec.js
index dd61143..d3c09cb 100644
--- a/index.spec.js
+++ b/index.spec.js
@@ -1,64 +1,118 @@
-const { ObjectPool } = require(".");
+"use strict";
+
+const ObjectPool = require(".");
 
 describe("GIVEN ObjectPool instance", () => {
   let pool;
 
+  const resolveArgument = "[Promise resolved]";
+
+  function factory() {
+    return new Promise((resolve) => {
+      setTimeout(() => resolve(resolveArgument), 500);
+    });
+  }
+
   beforeEach(() => {
-    pool = new ObjectPool(() => true);
+    pool = new ObjectPool(factory);
   });
 
   it("THEN It should create", () => {
     expect(pool).toBeTruthy();
   });
 
-  describe("WHEN pool.next is called", () => {
-    it("THEN even if objects size is 0", () => {
-      expect(pool.objects.size).toBe(0);
+  describe("WHEN pool.get is called", () => {
+    it("THEN even if pool.size is 0", () => {
+      expect(pool.size).toBe(0);
     });
 
-    it("THEN It should return new instance of object", () => {
-      expect(pool.next()).toBe(true);
+    it("THEN It should return new instance of factory call", () => {
+      expect(typeof pool.get()).toBe(typeof factory());
     });
 
-    it("THEN events.next should be emitted", async (done) => {
-      pool.events.on("next", () => done());
+    it("THEN events.get should be emitted", async (done) => {
+      pool.events.on("get", () => done());
 
-      pool.next();
+      pool.get();
     });
   });
 
-  describe("WHEN pool.back is called", () => {
-    it("THEN objects size should be greater than 0 afterwards", () => {
-      pool.back(false);
+  describe("WHEN pool.put is called", () => {
+    it("THEN pool.size should be greater than 0 afterwards", () => {
+      pool.put(false);
+
+      expect(pool.size).toBeGreaterThan(0);
+    });
+
+    it("THEN events.put should be emitted", async (done) => {
+      pool.events.on("put", () => done());
 
-      expect(pool.objects.size).toBeGreaterThan(0);
+      pool.put(null);
     });
+  });
+
+  describe("WHEN promise is `put` and then `get` again", () => {
+    it("THEN it still works as expected", async (done) => {
+      const once = pool.get();
+      const value = await once;
+
+      setTimeout(() => {
+        pool.put(once);
+
+        const again = pool.get();
+
+        expect(typeof again).toBe(typeof once);
+        expect(typeof value).toBe(typeof resolveArgument);
+
+        expect(value).toBe(resolveArgument);
 
-    it("THEN events.back should be emitted", async (done) => {
-      pool.events.on("back", () => done());
+        expect(Promise.resolve(once)).toBe(once);
+        expect(Promise.resolve(again)).toBe(again);
 
-      pool.back(null);
+        done();
+      }, 1000);
     });
   });
 
-  describe("WHEN pool.empty is called on non-empty pool", () => {
+  describe("WHEN pool.size is set to 0 on non-empty pool", () => {
     // prepare with data
     beforeEach(() => {
-      pool.back(null);
-      pool.back(null);
-      pool.back(null);
+      pool.put(null);
+      pool.put(null);
+      pool.put(null);
     });
 
-    it("THEN events.remove should be emitted for each item", async (done) => {
-      let count = pool.objects.size;
+    it("THEN events.delete should be emitted for each item", async (done) => {
+      let count = pool.size;
 
-      pool.events.on("remove", () => {
+      pool.events.on("delete", () => {
         if (!--count) {
-          done()
+          done();
         }
       });
 
-      pool.empty();
+      pool.size = 0;
+    });
+  });
+
+  describe("WHEN pool.size is set", () => {
+    const initialSize = 5;
+
+    // prepare with data
+    beforeEach(() => {
+      pool.size = initialSize;
+    });
+
+    it("THEN pool size adjusts and is being filled accordingly", () => {
+      pool.size = initialSize * 10;
+
+      expect(pool.size).toBe(initialSize * 10);
+    });
+
+    it("THEN pool size adjusts and is being trimmed accordingly", () => {
+      pool.size = 1;
+
+      expect(pool.size).toBe(1);
     });
   });
 });
diff --git a/package.json b/package.json
index 77c7d18..fc1e906 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@jacekpietal/object-pool",
-  "version": "1.0.2",
-  "description": "Object Pool manager for instantiating, getting, reuising and destroying objects in javascript (mostly for games)",
+  "version": "1.1.0",
+  "description": "zero-dependency Object Pool manager for instantiating, getting, reuising and destroying objects in javascript",
   "main": "index.js",
   "scripts": {
     "test": "jest"