Improve examples

Author: tshemsedinov

JavaScript/2-promise.js

@@ -1,5 +1,43 @@
 'use strict';
 
+// Pending
+
+const promise1 = new Promise((resolve, reject) => {
+  setTimeout(() => {
+    resolve('value1');
+  }, 0);
+});
+console.dir({ promise1 }); // Promise { <pending> }
+promise1.then(console.log); // 'value1' (delayed)
+
+// Immediate resolve
+
+const promise2 = new Promise(resolve => resolve('value2'));
+console.dir({ promise2 }); // Promise { 'value2' }
+promise2.then(console.log); // 'value2'
+
+// Immediate reject
+
+const promise3 = new Promise((resolve, reject) => {
+  reject(new Error('I have no value for you'));
+});
+console.dir({ promise3 }); // Promise { <rejected> Error... }
+promise3.then(console.log).catch(console.log); // Error...
+
+// Promise.resolve
+
+const promise4 = Promise.resolve('value4');
+console.log({ promise4 }); // Promise { 'value4' }
+promise4.then(console.log); // 'value4'
+
+// Promise.reject
+
+const promise5 = Promise.reject(new Error('I have no value for you'));
+console.dir({ promise5 }); // Promise { <rejected> Error... }
+promise5.then(console.log).catch(console.log); // Error...
+
+// Example with I/O
+
 const fs = require('fs');
 
 const readFile = (filename, encoding) =>

JavaScript/3-promisify.js

@@ -1,19 +1,49 @@
 'use strict';
 
+const promisify = fn => (...args) => new Promise((resolve, reject) => {
+  args.push((err, result) => {
+    if (err) reject(err);
+    else resolve(result);
+  });
+  fn(...args);
+});
+
 const fs = require('fs');
-const promisify = require('./promisify');
 
-const readFile = promisify(fs.readFile);
+const readFile1 = promisify(fs.readFile);
+
+readFile1('file1.txt', 'utf8')
+  .then(data => {
+    console.log(data.toString());
+    return readFile1('file2.txt', 'utf8');
+  })
+  .then(data => {
+    console.log(data.toString());
+    return readFile1('file3.txt', 'utf8');
+  })
+  .then(data => {
+    console.log(data.toString());
+  })
+  .catch(err => {
+    console.log(err);
+  });
+
+const util = require('util');
 
-readFile('file1.txt', 'utf8')
+const readFile2 = util.promisify(fs.readFile);
+
+readFile2('file1.txt', 'utf8')
   .then(data => {
     console.log(data.toString());
-    return readFile('file2.txt', 'utf8');
+    return readFile2('file2.txt', 'utf8');
   })
   .then(data => {
     console.log(data.toString());
-    return readFile('file3.txt', 'utf8');
+    return readFile2('file3.txt', 'utf8');
   })
   .then(data => {
     console.log(data.toString());
+  })
+  .catch(err => {
+    console.log(err);
   });

JavaScript/7-http.js

@@ -1,12 +1,11 @@
 'use strict';
 
-const httpGet = require('./get-json');
+const fetch = require('./6-fetch.js');
 
-const baseUrl = 'http://localhost:3000/';
-
-httpGet(baseUrl + 'person')
-  .then((data) => {
+fetch('http://localhost:3000/person')
+  .then(data => {
     console.log(data);
-    return httpGet(baseUrl + 'city');
   })
-  .then(console.log);
+  .catch(err => {
+    console.error(err);
+  });