JavaScript Arrays: Creating Lists and Working with Collection Data

const skills =["HTML", "CSS", "JavaScript"];
const prices =[499, 1299, 99];
const mixed =["text", 42, true, null, {
  id: 1
},[1, 2]];
// arrays hold ANYTHINGconst empty = [];                                            // an empty list

const arr1 = new Array(1, 2, 3);
// [1, 2, 3] ✅const arr2 = new Array(3);          // 😱 [empty × 3] — NOT [3]!

Array.of(3);
// [3] — the constructor fixed ✅Array.from("hello");         // ["h", "e", "l", "l", "o"] — iterables → array![..."abc"];                  // ["a", "b", "c"] — spread does it too (Lesson 14)

const skills =["HTML", "CSS", "JavaScript", "React"];
//                0        1          2           3   ← indexes
console.log(skills[0]);
// "HTML" — the FIRST item is index 0!console.log(skills[2]);    // "JavaScript"console.log(skills[3]);    // "React" — last item = length - 1console.log(skills[10]);   // undefined — beyond the edge (no error, Lesson 47 style 🤫)

console.log(skills.length);
// 4 — how many itemsconsole.log(skills[skills.length - 1]); // "React" — the classic "last item" patternconsole.log(skills.at(-1));           // "React" — the modern way! ✨ (negative = from the end)console.log(skills.at(-2));           // "JavaScript"

const cart =["Keyboard", "Mouse"];
cart[1] = "Gaming Mouse";
// ✏️ update existingcart[2] = "Monitor";             // ➕ add at a specific position
console.log(cart);
// ["Keyboard", "Gaming Mouse", "Monitor"]

const queue =["Amit"];
// 🚪 END of the array:queue.push("Priya");      // add at end     → ["Amit", "Priya"]queue.push("Riya");       //                → ["Amit", "Priya", "Riya"]queue.pop();              // remove from end → removes "Riya"
// 🚪 BEGINNING of the array:queue.unshift("Karan");   // add at start    → ["Karan", "Amit", "Priya"]queue.shift();            // remove from start → removes "Karan"
console.log(queue);
// ["Amit", "Priya"] ✅

// 💡 Bonus: pop/shift hand you the removed item:
const last =["a", "b", "c"].pop();
console.log(last);
// "c" — removed AND captured ✅

const letters =["a", "b", "c", "d", "e"];
console.log(letters.slice(1, 4));
// ["b", "c", "d"] — from index 1 up to (not incl.) 4
console.log(letters.slice(2));
// ["c", "d", "e"] — from index 2 to the end
console.log(letters.slice(-2));
// ["d", "e"] — negative = from the end
console.log(letters);
// ["a"…"e"] — original UNCHANGED ✅
const copy = letters.slice();
// 📄 a full shallow copy!

const months =["Jan", "Feb", "Mar", "Apr"];
months.splice(1, 1);
// at index 1, delete 1 item
console.log(months);
// ["Jan", "Mar", "Apr"] — "Feb" removed 🗑️
months.splice(1, 0, "February");
// at index 1, delete 0, INSERT here
console.log(months);
// ["Jan", "February", "Mar", "Apr"] ➕
months.splice(2, 1, "MARCH!");
// delete 1 at index 2 AND insert
console.log(months);
// ["Jan", "February", "MARCH!", "Apr"] 🔄