Add tasks

Author: tshemsedinov

JavaScript/Tasks/1-sync.js

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+'use strict';
+
+// Task: rewrite function to return result into sync callback
+
+// Change signature to: (items, callback(result))
+const total = (items) => {
+  let result = 0;
+  for (const item of items) {
+    result += item.price;
+  }
+  return result;
+};
+
+const electronics = [
+  { name: 'Laptop', price: 1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+// Use new signature total(electronics, (money) => ...)
+const money = total(electronics);
+console.log({ money });

JavaScript/Tasks/2-error.js

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+'use strict';
+
+// Task: return an error for items with negative price
+// Hint: use callback-last-error-first contract
+
+const total = (items, callback) => {
+  let result = 0;
+  for (const item of items) {
+    result += item.price;
+  }
+  callback(result);
+};
+
+const electronics = [
+  { name: 'Laptop', price: -1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+total(electronics, (money) => {
+  console.log({ money });
+});

JavaScript/Tasks/3-async.js

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+'use strict';
+
+// Task: rewrite `total` function to be async with JavaScript timers
+// Use `setInterval` and `clearInterval` to check next item each 1 second
+// Calculations will be executed asynchronously because of timers
+// Run `total` twice (as in example below) but in parallel
+// Print debug output for each calculation step (each second)
+//
+// Hint: example output:
+// { check: { item: { name: 'Laptop', price: 1500 } } }
+// { check: { item: { name: 'Laptop', price: 1500 } } }
+// { check: { item: { name: 'Keyboard', price: 100 } } }
+// { check: { item: { name: 'Keyboard', price: 100 } } }
+// { check: { item: { name: 'HDMI cable', price: 10 } } }
+// { check: { item: { name: 'HDMI cable', price: 10 } } }
+// { money: 1610 }
+// { money: 1610 }
+
+const total = (items, callback) => {
+  let result = 0;
+  for (const item of items) {
+    console.log({ check: { item } });
+    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 },
+];
+
+total(electronics, (error, money) => {
+  if (error) console.error({ error });
+  else console.log({ money });
+});
+
+total(electronics, (error, money) => {
+  if (error) console.error({ error });
+  else console.log({ money });
+});

JavaScript/Tasks/4-hell.js

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+'use strict';
+
+// Task: refactor callback hell code with named callbacks
+// Restriction: you can change code only in "Usage" section
+
+const getPurchase = (callback) => callback({
+  Electronics: [
+    { name: 'Laptop', price: 1500 },
+    { name: 'Keyboard', price: 100 },
+    { name: 'HDMI cable', price: 10 },
+  ],
+  Textile: [
+    { name: 'Bag', price: 50 },
+  ],
+});
+
+const iterateGroups = (order, callback) => {
+  for (const groupName in order) {
+    const group = order[groupName];
+    callback(group);
+  }
+};
+
+const groupTotal = (items, callback) => {
+  let total = 0;
+  for (const item of items) {
+    total += item.price;
+  }
+  callback(total);
+};
+
+const budget = (limit) => {
+  let balance = limit;
+
+  const withdraw = (value, callback) => {
+    const success = balance >= value;
+    if (success) balance -= value;
+    callback(success);
+  };
+
+  const rest = (callback) => callback(balance);
+
+  return { withdraw, rest };
+};
+
+// Usage
+
+const wallet = budget(1650);
+
+getPurchase((purchase) => {
+  let amount = 0;
+  iterateGroups(purchase, (group) => {
+    groupTotal(group, (subtotal) => {
+      wallet.withdraw(subtotal, (success) => {
+        if (success) amount += subtotal;
+        wallet.rest((balance) => {
+          console.log({ success, amount, subtotal, balance });
+        });
+      });
+    });
+  });
+});