diff --git a/JavaScript/Tasks/1-sync.js b/JavaScript/Tasks/1-sync.js
index 9939c4f..12a38e0 100644
--- a/JavaScript/Tasks/1-sync.js
+++ b/JavaScript/Tasks/1-sync.js
@@ -3,12 +3,13 @@
 // Task: rewrite function to return result into sync callback
 
 // Change signature to: (items, callback(result))
-const total = (items) => {
+const total = (items, callback) => {
   let result = 0;
   for (const item of items) {
     result += item.price;
   }
-  return result;
+  callback(result);
+
 };
 
 const electronics = [
@@ -18,5 +19,4 @@ const electronics = [
 ];
 
 // Use new signature total(electronics, (money) => ...)
-const money = total(electronics);
-console.log({ money });
+total(electronics, (money) => console.log(money));
diff --git a/JavaScript/Tasks/2-error.js b/JavaScript/Tasks/2-error.js
index 5badbcf..e620a3a 100644
--- a/JavaScript/Tasks/2-error.js
+++ b/JavaScript/Tasks/2-error.js
@@ -8,7 +8,10 @@ const total = (items, callback) => {
   for (const item of items) {
     result += item.price;
   }
-  callback(result);
+  if(result < 0){
+    callback(new Error("Price is negative"), result)
+  }  
+  callback(null, result);
 };
 
 const electronics = [
@@ -17,6 +20,10 @@ const electronics = [
   { name: 'HDMI cable', price: 10 },
 ];
 
-total(electronics, (money) => {
+total(electronics, (err, money) => {
+  if(err){
+    console.error(err.message, money)
+    throw err
+  }
   console.log({ money });
 });
diff --git a/JavaScript/Tasks/3-async.js b/JavaScript/Tasks/3-async.js
index 626fe64..1f94823 100644
--- a/JavaScript/Tasks/3-async.js
+++ b/JavaScript/Tasks/3-async.js
@@ -16,17 +16,30 @@
 // { money: 1610 }
 // { money: 1610 }
 
-const total = (items, callback) => {
+const total = async (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);
+  let index = 0;
+  await new Promise((res, rej)=> {
+      const timerId = setInterval(()=>{
+        const item = items[index];
+        if(!item){
+          clearInterval(timerId)
+          res();
+          return
+        } 
+        console.log({ check: { item } });
+        if (item.price < 0) {
+          rej(new Error('Negative price is not allowed'));
+          clearInterval(timerId)
+          return;
+        }
+        result += item.price;
+        index+=1;
+      }, 1000)
+  
+ 
+  }).then(()=>callback(null, result)).catch(err=>callback(err))
+  
 };
 
 const electronics = [
diff --git a/JavaScript/Tasks/4-hell.js b/JavaScript/Tasks/4-hell.js
index 0985775..a197773 100644
--- a/JavaScript/Tasks/4-hell.js
+++ b/JavaScript/Tasks/4-hell.js
@@ -47,16 +47,22 @@ const budget = (limit) => {
 
 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 });
-        });
-      });
+const processGroupTotal = (amount) => (subtotal) => {
+  wallet.withdraw(subtotal, (success) => {
+    if (success) amount += subtotal;
+    wallet.rest((balance) => {
+      console.log({ success, amount, subtotal, balance });
     });
   });
-});
+}
+
+const processIterateGroups = (amount) =>(group) => {
+    groupTotal(group, processGroupTotal(amount) );
+}
+
+const processPurchase = (purchase) => {
+  let amount = 0;
+  iterateGroups(purchase, processIterateGroups(amount));
+}
+
+getPurchase(processPurchase);
diff --git a/JavaScript/Tasks/5-errors.js b/JavaScript/Tasks/5-errors.js
index f5f9769..43549ef 100644
--- a/JavaScript/Tasks/5-errors.js
+++ b/JavaScript/Tasks/5-errors.js
@@ -14,34 +14,39 @@ const calculateSubtotal = (goods, callback) => {
   let amount = 0;
   for (const item of goods) {
     if (typeof item.name !== 'string') {
-      throw new Error('Noname in item in the bill');
+     return callback(new Error('Noname in item in the bill')) 
     }
     if (typeof item.price !== 'number') {
-      throw new Error(`${item.name} price expected to be number`);
+      return callback(new Error(`${item.name} price expected to be number`));
     }
     if (item.price < 0) {
-      throw new Error(`Negative price for ${item.name}`);
+      return callback(new Error(`Negative price for ${item.name}`));
     }
     amount += item.price;
   }
-  callback(amount);
+  callback(null, amount);
 };
 
 const calculateTotal = (order, callback) => {
   const expenses = new Map();
   let total = 0;
-  const calc = (groupName) => (amount) => {
-    total += amount;
-    expenses.set(groupName, amount);
+  const calc = (groupName) => (err, amount) => {
+    if(err){
+      return callback(err);
+    } else {
+      total += amount;
+      expenses.set(groupName, amount);
+    }
+    
   };
   for (const groupName in order) {
     const goods = order[groupName];
     calculateSubtotal(goods, calc(groupName));
     if (total > MAX_PURCHASE) {
-      throw new Error('Total is above the limit');
+      return callback(new Error('Total is above the limit'));
     }
   }
-  return callback({ total, expenses });
+  return callback(null, { total, expenses });
 };
 
 const purchase = {
@@ -56,12 +61,16 @@ const purchase = {
   ],
 };
 
-try {
+
   console.log(purchase);
-  calculateTotal(purchase, (bill) => {
-    console.log(bill);
+  calculateTotal(purchase, (err, bill) => {
+    
+    if(err){
+      console.log('Error detected');
+      console.error(err);
+    } else {
+       console.log(bill);
+    }
+   
   });
-} catch (error) {
-  console.log('Error detected');
-  console.error(error);
-}
+