Global state with modules singleton example

Author: tshemsedinov

NodeJS/0-global-state/main.js

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+'use strict';
+
+const state = require('./state.js');
+const unit1 = require('./unit1.js');
+const unit2 = require('./unit2.js');
+
+const INITIAL_STATE = {
+  time: Date.now(),
+  counter: 0,
+};
+
+unit1.restore(INITIAL_STATE);
+
+setInterval(() => {
+  state.counter++;
+  unit2.show();
+  unit1.save();
+}, 1000);

NodeJS/0-global-state/state.js

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+'use strict';
+
+const state = {};
+
+module.exports = state;

NodeJS/0-global-state/unit1.js

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+'use strict';
+
+const fs = require('node:fs').promises;
+const state = require('./state.js');
+
+const fileName = './state.json';
+
+const save = async () => {
+  const data = JSON.stringify(state);
+  await fs.writeFile(fileName, data);
+};
+
+const restore = async (initialState) => {
+  try {
+    const data = await fs.readFile(fileName);
+    const stored = JSON.parse(data);
+    Object.assign(state, stored);
+  } catch {
+    Object.assign(state, initialState);
+  }
+};
+
+module.exports = { save, restore };

NodeJS/0-global-state/unit2.js

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+'use strict';
+
+const state = require('./state.js');
+
+const show = () => {
+  console.table(state);
+};
+
+module.exports = { show };