Add more examples

Author: tshemsedinov

JavaScript/Tasks/3-constructor.js

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+'use strict';
+
+// Task: rewrite class Basket to class Total with async constructor
+// Constructor call example:
+//   const total = await new Total(electronics);
+//   console.log({ total });
+
+class Basket {
+  #items = null;
+
+  constructor(items) {
+    this.#items = items;
+  }
+
+  total(callback) {
+    let result = 0;
+    for (const item of this.#items) {
+      if (item.price < 0) {
+        callback(new Error('Negative price is not allowed'));
+        return;
+      }
+      result += item.price;
+    }
+    callback(null, result);
+  }
+}
+
+const electronics = [
+  { name: 'Laptop', price: 1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+const basket = new Basket(electronics);
+basket.total((error, money) => {
+  if (error) console.error({ error });
+  else console.log({ money });
+});

JavaScript/Tasks/4-default.js

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+'use strict';
+
+// Task: optimize `total` call with default value 0 (as in example)
+// to have one-line solution - 1 line instead of 5 lines
+// (call and default value in one line)
+
+// Do not change code before usage block
+
+const total = async (items) => {
+  let result = 0;
+  for (const item of items) {
+    if (item.price < 0) {
+      throw new Error('Negative price is not allowed');
+    }
+    result += item.price;
+  }
+  return result;
+};
+
+const electronics = [
+  { name: 'Laptop', price: -1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+// Usage block: change just following code
+
+(async () => {
+  let money = 0;
+  try {
+    money = await total(electronics);
+  } catch {
+  }
+  console.log({ money });
+})();

JavaScript/Tasks/5-exists.js

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+'use strict';
+
+// Task: optimize `fileExists` function to one-liner
+// Do not change "Usage" section, edit just "Implementation"
+
+const fs = require('node:fs');
+
+// Implementation
+
+const fileExists = async (name) => {
+  try {
+    await fs.promises.access(name);
+    return true;
+  } catch {
+    return false;
+  }
+};
+
+// Usage
+
+(async () => {
+  const name = 'file-name.ext';
+  const exists = await fileExists(name);
+  console.log({ name, exists });
+})();
+
+(async () => {
+  const name = '5-exists-problem.js';
+  const exists = await fileExists(name);
+  console.log({ name, exists });
+})();