Add closure state example

Author: tshemsedinov

NodeJS/2-closure/main.js

@@ -0,0 +1,10 @@
+'use strict';
+
+const unit1 = require('./unit1.js');
+const unit2 = require('./unit2.js');
+
+setTimeout(() => {
+  unit2();
+  const res = unit1();
+  console.log({ res });
+}, 100);

NodeJS/2-closure/unit1.js

@@ -0,0 +1,24 @@
+'use strict';
+
+const fs = require('node:fs');
+
+const { readFile } = fs;
+
+let calls = 0;
+let callbacks = 0;
+
+fs.readFile = (fileName, callback) => {
+  calls++;
+  console.log('call');
+  readFile(fileName, (error, data) => {
+    callbacks++;
+    console.log('callback');
+    callback(error, data);
+  });
+};
+
+module.exports = () => {
+  console.log('unit1');
+  console.log({ calls, callbacks });
+  return { calls, callbacks };
+};

NodeJS/2-closure/unit2.js

@@ -0,0 +1,15 @@
+'use strict';
+
+const fs = require('node:fs');
+
+fs.readFile('./main.js', (error, data) => {
+  if (error) {
+    console.log({ error });
+  } else {
+    console.log({ data });
+  }
+});
+
+module.exports = () => {
+  console.log('unit2');
+};