diff --git a/playground/4-callbacks.js b/playground/4-callbacks.js
index cf643df..bcb21f8 100644
--- a/playground/4-callbacks.js
+++ b/playground/4-callbacks.js
@@ -1,33 +1,14 @@
-// setTimeout(() => {
-//   console.log('Two seconds are up')
-// }, 2000)
-//
-// const names = ['Jason', 'Jen', 'Jess']
-// const shortNames = names.filter((name) => {
-//   return name.length <= 4
-// })
-//
-// const geocode = (address, callback) => {
-//   setTimeout(() => {
-//     const data = {
-//       latitude: 0,
-//       longitude: 0
-//     }
-//
-//     callback(data)
-//   }, 2000)
-// }
-//
-// geocode('Philadelphia', (data) => {
-//   console.log(data)
-// })
-
-const add = (x, y, callback) => {
+const doWorkCallback = (callback) => {
   setTimeout(() => {
-    callback(x + y)
+    //callback('This is my error!', undefined)
+    callback(undefined, [1, 4, 7])
   }, 2000)
 }
 
-add(1, 4, (sum) => {
-    console.log(sum) // Should print: 5
+doWorkCallback((error, result) => {
+  if (error) {
+    return console.log(error)
+  }
+
+  console.log(result)
 })
diff --git a/playground/8-promises.js b/playground/8-promises.js
new file mode 100644
index 0000000..30d467e
--- /dev/null
+++ b/playground/8-promises.js
@@ -0,0 +1,12 @@
+const doWorkPromise = new Promise((resolve, reject) => {
+  setTimeout(() => {
+    reject('Things went wrong!')
+    // resolve([7, 4, 1])
+  }, 2000)
+})
+
+doWorkPromise.then((result) => {
+  console.log('Success!', result)
+}).catch((error) => {
+  console.log('Error!', error)
+})