Add tasks

Author: tshemsedinov

JavaScript/Tasks/1-adapter.js

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+'use strict';
+
+// Task: create Promise-returning adapter function `totalAsync`
+// Do not change function `total` contract, just call `total` from
+// `totalAsync` and convert contracts
+
+// Should not be changed
+const total = (items, callback) => {
+  let result = 0;
+  for (const item of items) {
+    if (item.price < 0) {
+      callback(new Error('Negative price is not allowed'));
+      return;
+    }
+    result += item.price;
+  }
+  callback(null, result);
+};
+
+// const totalAsync = (items) => new Promise...
+
+const electronics = [
+  { name: 'Laptop', price: 1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+// Also rewrite call, use .then instead of callback
+total(electronics, (error, money) => {
+  if (error) console.error({ error });
+  else console.log({ money });
+});

JavaScript/Tasks/2-promise.js

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+'use strict';
+
+// Task: change `iterate` contract from chainable callbacks
+// to Promise (chainable or you can call it with await syntax)
+
+const iterate = (items) => {
+  let index = 0;
+  const chain = {
+    next: (callback) => {
+      if (index < items.length) {
+        callback(items[index++]);
+      }
+      return chain;
+    }
+  };
+  return chain;
+};
+
+const electronics = [
+  { name: 'Laptop', price: 1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+// Use await syntax to get items
+iterate(electronics).next((item) => {
+  console.log(item);
+}).next((item) => {
+  console.log(item);
+}).next((item) => {
+  console.log(item);
+});

JavaScript/Tasks/3-reject.js

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+'use strict';
+
+// Task: support rejection with an error, if no more items in
+// `items` array are available to return with `.next()`
+// Change throwing error to returning rejected Promise.
+
+const iterate = (items) => {
+  let index = 0;
+  return {
+    next: () => new Promise((fulfill) => {
+      if (index < items.length) {
+        return fulfill(items[index++]);
+      }
+      throw new Error('No more items to iterate');
+    })
+  };
+};
+
+const electronics = [
+  { name: 'Laptop', price: 1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+(async () => {
+  const items = iterate(electronics);
+  const item1 = await items.next();
+  console.log(item1);
+  const item2 = await items.next();
+  console.log(item2);
+  const item3 = await items.next();
+  console.log(item3);
+  const item4 = await items.next();
+  console.log(item4);
+})();

JavaScript/Tasks/4-chain.js

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+'use strict';
+
+// Task: here is given code you can't touch but you need to
+// write solution below to sum given prices (wrapped in promises).
+// Use Promise.all to resolve promises.
+// Use functions: `formatMoney` and `sum` as utilities.
+// Additional task: add .catch and .finally blocks in chain
+
+// Do not touch following code
+
+const CURRENCY_RATE = 1.09;
+
+const convert = ({ price }) => Promise.resolve(price * CURRENCY_RATE);
+
+const electronics = [
+  { name: 'Laptop', price: 1500 },
+  { name: 'Keyboard', price: 100 },
+  { name: 'HDMI cable', price: 10 },
+];
+
+const prices = electronics.map(convert);
+
+const formatMoney = (x) => parseFloat(x.toFixed(2));
+
+const sum = (a, b) => a + b;
+
+// Write solution below