Create exercise_03.js

Author: Siyuan Gao

Lesson09/exercise_03.js

@@ -0,0 +1,43 @@
+const fs = require('fs');
+
+fs.writeFile('test.txt', 'Hello world', (error) => {
+    if (error) {
+        console.error(error);
+        return;
+    }
+    console.log('Write complete');
+});
+
+// After running above code:
+fs.readFile('test.txt', 'utf-8', (error, data) => {
+    if (error) {
+        console.error(error);
+    }
+    console.log(data);
+});
+
+// Read from no file
+fs.readFile('nofile.txt', 'utf-8', (error, data) => {
+    if (error) {
+        console.error(error);
+    }
+    console.log(data);
+});
+
+// Readfile promisified
+function readFile(file, options) {
+    return new Promise((resolve, reject) => {
+        fs.readFile(file, options, (error, data) => {
+            if (error) {
+                return reject(error);
+            }
+            resolve(data);
+        })
+    })
+}
+
+// New usage after Node 10
+const fsPromises = require('fs').promises;
+fsPromises.readFile('test.txt', 'utf-8').then(console.log);
+
+fsPromises.stat('test.txt').then(console.log);