Did array and object question

injora/answers.js

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+/*
+ * ======================================================
+ *  ADVANCED JAVASCRIPT ASSIGNMENT
+ *  Arrays, Objects, Callbacks, Promises, Async/Await, Timers
+ *  Each question has space for writing the solution.
+ *  Create name of your folder name , and then answer these
+     questions in seperate file. 
+ * ======================================================
+ */
+
+//
+// ======================================================
+//                CATEGORY 1: MEDIUM LEVEL
+// ======================================================
+//
+
+// ---------- ARRAYS (1–5) ----------
+
+// 1. Write a function that returns the second largest number in an array.
+// Solution:
+const sc = (arr)=>{
+    mx = arr[0]
+    for(let i = 0;i<arr.length;i++){
+        if (arr[i]>mx){
+            mx = arr[i]
+        }
+        i1=i
+    }
+    arr.splice(i1,1)
+    mx2 = arr[0]
+    for(let i = 0;i<arr.length;i++){
+        if (arr[i]>mx2){
+            mx2 = arr[i]
+        }
+    }
+    return mx2
+}
+
+
+// 2. Return all strings with length > 4 from an array.
+// Solution:
+
+const four =(arr)=>{
+    narr=[]
+    for(let i =0;i<arr.length;i++){
+        if(arr[i].length>4){
+            narr.push(arr[i])
+        }
+    }
+    return narr
+}
+
+// 3. Convert an array of numbers to their squares using .map().
+// Solution:
+const map =(arr)=>{
+    const sq = arr.map(num=>num**2)
+    return sq
+}
+
+
+
+// 4. Remove duplicate values from an array (without using Set).
+// Solution:
+
+const dup = (arr)=>{
+    for(let i = 0;i<arr.length;i++){
+        for(let j = i+1;j<arr.length;j++){
+            if(arr[i]==arr[j]){
+                arr.splice(j,1)
+            }
+        }
+    }
+    return arr
+}
+
+// 5. Count how many times each element appears in an array (return an object).
+// Solution:
+
+const count=(arr,ele)=>{
+    let count = 0
+    for(let i = 0;i<arr.length;i++){
+        if(arr[i]==ele){
+            count+=1
+        }
+    }
+    return count
+}
+
+// ---------- OBJECTS (6–10) ----------
+
+// 6. Write a function that returns all keys of an object in an array.
+// Solution:
+const key = (arr)=>{
+    return Object.keys(arr)
+}
+
+
+// 7. Given an object of item prices, return the total cost.
+// Solution:
+const total = (obj) => {
+    return Object.values(obj).reduce((sum, price) => sum + price, 0);
+}
+
+
+// 8. Write a function that checks if an object is empty.
+// Solution:
+const empty = (obj) => {
+    return Object.keys(obj).length === 0;
+}
+
+
+
+// 9. Merge two objects without using the spread operator.
+// Solution:
+const add = (obj1, obj2)=>{
+    const result = {};
+    for (let key in obj1) {
+        result[key] = obj1[key];
+    }
+    for (let key in obj2) {
+        result[key] = obj2[key];
+    }
+    return result;
+};
+
+
+
+// 10. Create an object with a method that returns "Hello, <name>" using this.
+// Solution:
+const greet = {
+    name: "injora",
+    hello() {
+        return `Hello, ${this.name}`;
+    }
+};
+
+console.log(greeter.sayHello());
+
+
+
+
+
+//
+// ======================================================
+//                   CATEGORY 2: HARD LEVEL
+// ======================================================
+//
+
+// ---------- CALLBACKS (1–2) ----------
+
+// 1. Write a function repeatTask(n, task) that runs a callback n times.
+// Solution:
+
+
+
+// 2. Simulate fetching a user with a callback after a delay.
+// Solution:
+
+
+
+
+// ---------- PROMISES (3–5) ----------
+
+// 3. Convert a callback-based function into a promise-based one.
+// Solution:
+
+
+
+// 4. Write loadData() that resolves in 2s or rejects randomly (50% chance).
+// Solution:
+
+
+
+// 5. Chain: loadUser → loadPosts → loadComments.
+// Each returns a promise.
+// Solution:
+
+
+
+
+// ---------- ASYNC/AWAIT (6–7) ----------
+
+// 6. Rewrite question 5 using async/await instead of .then().
+// Solution:
+
+
+
+// 7. Write an async function that fetches two promises in parallel.
+// Solution:
+
+
+
+
+// ---------- TIMERS + LOGIC (8–10) ----------
+
+// 8. Print numbers from 10 down to 1 using a timer, then print "Done".
+// Solution:
+
+
+
+// 9. Implement a throttled function that runs once every 2 seconds.
+// Solution:
+
+
+
+// 10. Implement a debounced function that runs only when typing stops for 500ms.
+// Solution:
+
+
+
+
+
+//
+// ======================================================
+//                CATEGORY 3: BONUS QUESTIONS
+// ======================================================
+//
+
+// ---------- ARRAYS & OBJECTS (1–3) ----------
+
+// 1. Convert an array of users into an object using their id as the key.
+// Solution:
+const id = (arr) => {
+  const res = {};
+
+  for (let i = 0;i < arr.length;i++) {
+    const user= arr[i];
+    res[user.id] = user;
+  }
+
+  return res;
+}
+
+
+
+// 2. Given students with marks, return the top 3 scorers.
+// Solution:
+const three = (res) => {
+    let arr = [...res];
+    for (let i = 0; i < arr.length; i++) {
+        for (let j = i + 1; j < arr.length; j++) {
+            if (arr[i].marks < arr[j].marks) {
+                let temp = arr[i];
+                arr[i] = arr[j];
+                arr[j] = temp;
+            }
+        }
+    }
+    let result = [];
+    for (let i = 0; i < 3 && i < arr.length; i++) {
+        result.push(arr[i]);
+    }
+    return result;
+};
+console.log(three(res));
+
+
+
+
+// 3. Flatten [[1,2],[3,4],[5]] into [1,2,3,4,5] without using .flat().
+// Solution:
+const arr = [[1,2],[3,4],[5]];
+let flat = [];
+
+for (let lis of arr) {
+    for (let ele of lis) {
+        flattened.push(ele);
+    }
+}
+console.log(flat);
+
+
+
+
+// ---------- CALLBACKS / PROMISES / ASYNC (4–6) ----------
+
+// 4. Create retry(fn, attempts) that retries a failing promise.
+// Solution:
+
+
+
+// 5. Create a delay(ms) function and print numbers 1 to 5 with pauses.
+// Solution:
+
+
+
+// 6. Run two async tasks but fail fast if either rejects.
+// Solution:
+
+
+
+
+// ---------- TIMERS / LOGIC (7–10) ----------
+
+// 7. Build a clock that prints the current time every second.
+// Solution:
+
+
+
+// 8. Build a function that measures how long another function takes to run.
+// Solution:
+
+
+
+// 9. Create a countdown timer with pause, resume, and reset.
+// Solution:
+
+
+
+// 10. Explain the output order of:
+console.log("A");
+setTimeout(() => console.log("B"), 0);
+Promise.resolve().then(() => console.log("C"));
+console.log("D");
+// Write explanation here:
+// first a because a is in a simple console log and js runs line by line
+// then d same reason as above
+//then c because 
+
+
+
+
+//
+// ======================================================
+//                      MINI PROJECTS
+// ======================================================
+//
+
+// ---------- PROJECT 1: Task Scheduler ----------
+// Build a small task scheduler that:
+// - Accepts tasks
+// - Schedules them using setTimeout
+// - Prints "Task <name> executed"
+// - Allows canceling tasks
+// Solution starter:
+
+
+
+
+
+
+// ---------- PROJECT 2: Mini Quiz App ----------
+// Requirements:
+// - Store questions in an array of objects
+// - 10-second timer per question
+// - Auto-move to next question
+// - Show final score
+// Solution starter:
+
+
+
+
+
+