diff --git a/01-js/easy/anagram.js b/01-js/easy/anagram.js
index 8184c83083..8fa71fee5f 100644
--- a/01-js/easy/anagram.js
+++ b/01-js/easy/anagram.js
@@ -6,6 +6,31 @@
 
 function isAnagram(str1, str2) {
 
+  if(str1.length !== str2.length) return false;
+
+  const countAnagram = {};
+
+  for(const char of str1) {
+    const str = char.toLowerCase();
+    if(countAnagram[str]) {
+      countAnagram[str]++;
+    }else{
+      countAnagram[str] = 1;
+    }
+  }
+
+  for(const char of str2) {
+    const str = char.toLowerCase();
+    if(countAnagram[str]) {
+      if(countAnagram[str] === 1) {
+        delete countAnagram[str];
+      }else {
+        countAnagram[str]--;
+      }
+    }
+  }
+
+  return Object.keys(countAnagram).length === 0;
 }
 
 module.exports = isAnagram;
diff --git a/01-js/easy/expenditure-analysis.js b/01-js/easy/expenditure-analysis.js
index 09c4013040..d801952166 100644
--- a/01-js/easy/expenditure-analysis.js
+++ b/01-js/easy/expenditure-analysis.js
@@ -14,7 +14,20 @@
 */
 
 function calculateTotalSpentByCategory(transactions) {
-  return [];
+  const result = transactions.reduce((acc, item) => {
+    if(acc[item.category]) {
+      acc[item.category] = acc[[item.category]] + item.price;
+    }else{
+      acc[item.category] = item.price;
+    }
+    return acc;
+  }, {});
+
+  return Object.keys(result).map((item) => ({
+    category: item,
+    totalSpent: result[item]
+  }))
+  
 }
 
 module.exports = calculateTotalSpentByCategory;
diff --git a/01-js/easy/findLargestElement.js b/01-js/easy/findLargestElement.js
index 33278de43a..8168e34cce 100644
--- a/01-js/easy/findLargestElement.js
+++ b/01-js/easy/findLargestElement.js
@@ -6,7 +6,11 @@
 */
 
 function findLargestElement(numbers) {
-    
+    if(!numbers.length) return undefined;
+    return numbers.reduce((acc, item) => {
+        if(item > acc) acc = item;
+        return acc;
+    }, Number.NEGATIVE_INFINITY)
 }
 
 module.exports = findLargestElement;
\ No newline at end of file
diff --git a/01-js/hard/calculator.js b/01-js/hard/calculator.js
index fb60142b79..fe72381edf 100644
--- a/01-js/hard/calculator.js
+++ b/01-js/hard/calculator.js
@@ -16,6 +16,138 @@
   Once you've implemented the logic, test your code by running
 */
 
-class Calculator {}
+class Calculator {
+  result;
+
+  constructor() {
+    this.result = 0;
+  }
+
+  add(num) {    
+    this.result += num;
+  }
+
+  sub(num) {
+    this.result -= num;
+  }
+
+  multiply(num) {
+    this.result *= num;
+  }
+
+  divide(num) {
+    this.result /= num;
+  }
+
+  clear() {
+    this.result = 0;
+  }
+
+  getResult() {
+    return this.result;
+  }
+
+  calculate(exp) {
+    const tokens = exp.split(" ");
+    const stack = [];
+    const precedence = {
+      "+": 1,
+      "-": 1,
+      "*": 2,
+      "/": 2,
+    };
+
+    for (const token of tokens) {
+      if (!isNaN(token)) {
+        stack.push(Number(token));
+      } else if (token in precedence) {
+        while (
+          stack.length > 0 &&
+          precedence[stack[stack.length - 1]] >= precedence[token]
+        ) {
+          const op = stack.pop();
+          const b = stack.pop();
+          const a = stack.pop();
+          switch (op) {
+            case "+":
+              stack.push(a + b);
+              break;
+            case "-":
+              stack.push(a - b);
+              break;
+            case "*":
+              stack.push(a * b);
+              break;
+            case "/":
+              stack.push(a / b);
+              break;
+          }
+        }
+        stack.push(token);
+      } else if (token === "(") {
+        stack.push(token);
+      } else if (token === ")") {
+        while (stack.length > 0 && stack[stack.length - 1] !== "(") {
+          const op = stack.pop();
+          const b = stack.pop();
+          const a = stack.pop();
+          switch (op) {
+            case "+":
+              stack.push(a + b);
+              break;
+            case "-":
+              stack.push(a - b);
+              break;
+            case "*":
+              stack.push(a * b);
+              break;
+            case "/":
+              stack.push(a / b);
+              break;
+          }
+        }
+        stack.pop();
+      } else {
+        throw new Error("Invalid character: " + token);
+      }
+    }
+    while (stack.length > 0) {
+      const op = stack.pop();
+      const b = stack.pop();
+      const a = stack.pop();
+      switch (op) {
+        case "+":
+          stack.push(a + b);
+          break;
+        case "-":
+          stack.push(a - b);
+          break;
+        case "*":
+          stack.push(a * b);
+          break;
+        case "/":
+          stack.push(a / b);
+          break;
+      }
+    }
+    return stack[0];
+  }
+  
+}
+
+
+const calc = new Calculator();
+calc.add(10);
+console.log(calc.getResult());
+calc.sub(2);
+console.log(calc.getResult());
+calc.multiply(6);
+console.log(calc.getResult());
+calc.divide(2);
+console.log(calc.getResult());
+calc.clear();
+console.log(calc.getResult());
+
+
 
 module.exports = Calculator;
diff --git a/01-js/hard/todo-list.js b/01-js/hard/todo-list.js
index 381d6d0754..fba225a18d 100644
--- a/01-js/hard/todo-list.js
+++ b/01-js/hard/todo-list.js
@@ -12,6 +12,60 @@
 
 class Todo {
 
+  todos;
+  constructor(){
+    this.todos = [];
+  }
+
+  add(todo) {
+    this.todos.push(todo);
+  }
+
+  remove(index) {
+    const todos = this.todos.filter((i, idx) => idx !== index);
+    this.todos = todos;
+  }
+
+  update(idx, updatedTodo) {
+    const todos = this.todos.map((item, index) => {
+      if(index === idx) {
+        return {
+          ...updatedTodo
+        }
+      }
+      return item;
+    })
+    this.todos = todos;
+  }
+
+  getAll() {
+    return this.todos;
+  }
+
+  get(index) {
+    return this.todos.find((i, idx) => idx === index);
+  }
+
+  clear() {
+    this.todos = [];
+  }
 }
 
+
+const todos = new Todo();
+todos.add({id:1, name:'item 1'});
+todos.add({id:1, name:'item 3'});
+todos.add({id:1, name:'item 2'});
+todos.add({id:1, name:'item 4'});
+todos.add({id:1, name:'item 5'});
+console.log(todos.getAll());
+console.log(todos.get(3));
+todos.update(1, {id: 2, name: 'item 2'})
+todos.remove(3)
+todos.clear()
+todos.add({id:1, name:'item 5'});
+console.log(todos.getAll());
+
+
+
 module.exports = Todo;
diff --git a/01-js/medium/countVowels.js b/01-js/medium/countVowels.js
index 49db425d63..ab96185cd9 100644
--- a/01-js/medium/countVowels.js
+++ b/01-js/medium/countVowels.js
@@ -6,7 +6,12 @@
 */
 
 function countVowels(str) {
-    // Your code here
+    let count = 0;
+    for(const char of str) {
+      const vowels = ['a', 'e', 'i', 'o', 'u'];
+      if(vowels.includes(char.toLowerCase())) count++;
+    }
+    return count;
 }
 
 module.exports = countVowels;
\ No newline at end of file
diff --git a/01-js/medium/palindrome.js b/01-js/medium/palindrome.js
index 3f3b9adadb..f3be196789 100644
--- a/01-js/medium/palindrome.js
+++ b/01-js/medium/palindrome.js
@@ -4,6 +4,23 @@
 */
 
 function isPalindrome(str) {
+
+  let newString = '';
+  for(const s of str) {
+    const ch = s.toLowerCase();
+    if((ch >= 'a' && ch <= 'z')) {
+      newString += ch;
+    }
+  } 
+  
+  let i = 0, j = newString.length - 1;
+  while(i <= j) {
+    const ch1 = newString.charAt(i);
+    const ch2 = newString.charAt(j);
+    if(ch1 !== ch2) return false;
+    i++;
+    j--;
+  }
   return true;
 }
 
diff --git a/01-js/medium/times.js b/01-js/medium/times.js
index ea2d4c170a..d9ae7e2e1c 100644
--- a/01-js/medium/times.js
+++ b/01-js/medium/times.js
@@ -9,5 +9,18 @@ There is no automated test for this one, this is more for you to understand time
 */
 
 function calculateTime(n) {
-    return 0.01;
-}
\ No newline at end of file
+    const start = Date.now();
+    let sum = 0;
+    for(let i = 1; i <= n; i++) {
+        sum += i;
+    }
+    const end = Date.now();
+    const timeInSeconds = (end - start) / 1000;
+    console.log(`Total time = ${timeInSeconds} seconds`);
+    return sum;
+}
+
+console.log(calculateTime(100));
+console.log(calculateTime(100000));
+console.log(calculateTime(1000000000));
+