⚡ JavaScript Lesson 02 — Conditions

1. if / else if / else

let score = 75

if (score >= 80) {
  console.log("A grade")
} else if (score >= 70) {
  console.log("B grade")    // ← ဒါ ထွက်မယ်
} else if (score >= 60) {
  console.log("C grade")
} else {
  console.log("Fail")
}

2. Ternary Operator — Short if/else

// ပုံမှန် if/else
let age = 18
if (age >= 18) {
  status = "Adult"
} else {
  status = "Minor"
}

// Ternary operator (one-liner)
let status = age >= 18 ? "Adult" : "Minor"
//                    ↑         ↑
//              condition   else part
//                         (true part)

// Nested ternary (use sparingly)
let grade = score >= 80 ? "A" : score >= 60 ? "B" : "C"

3. switch / case

let day = "Monday"

switch (day) {
  case "Monday":
    console.log("တနင်္လာ — school day")
    break                    // ← break မပါရင် next case ဆက်သွားမယ်!
  case "Saturday":
  case "Sunday":             // ← တစ်ခုထက်ပိုတဲ့ case share နိုင်
    console.log("Weekend!")
    break
  default:                   // ← else like
    console.log("Weekday")
}

4. Logical Operators

// && (AND) — နှစ်ခုလုံး true ဖြစ်မှ true
let age = 20
let hasID = true
if (age >= 18 && hasID) {
  console.log("Access granted")
}

// || (OR) — တစ်ခုပဲ true ဖြစ်ရင် true
let isMember = false
let isPremium = true
if (isMember || isPremium) {
  console.log("Can access")
}

// ! (NOT)
let isClosed = false
if (!isClosed) {
  console.log("Shop is open!")
}

// Short-circuit evaluation
// && — left false ဆိုရင် right မစစ်
let user = null
let name = user && user.name  // null

// || — default value
let input = ""
let val = input || "default"  // "default"

// ?? (nullish coalescing — null/undefined only)
let config = null
let setting = config ?? "default"  // "default"

// Practical examples
function greet(name) {
  name = name || "Guest"
  return `Hello, ${name}!`
}
greet()         // "Hello, Guest!"
greet("Min")    // "Hello, Min!"

5. Truthy & Falsy Values

// Falsy values — if condition မှာ false လိုပဲ မှတ်ယူ
if (false)     { } // false
if (0)         { } // 0
if ("")        { } // empty string
if (null)      { } // null
if (undefined) { } // undefined
if (NaN)       { } // NaN

// Everything else is Truthy:
if (1)         { } // ✅ true
if ("hello")   { } // ✅ true
if ([])        { } // ✅ true (empty array!)
if ({})        { } // ✅ true (empty object!)

6. Real-world Example — Login Check

function login(username, password) {
  if (!username || !password) {
    return "❌ Username နဲ့ Password ထည့်ပါ"
  }
  if (username.length < 3) {
    return "❌ Username အနည်းဆုံး 3 လုံး"
  }
  if (password.length < 6) {
    return "❌ Password အနည်းဆုံး 6 လုံး"
  }
  if (username === "admin" && password === "admin123") {
    return "✅ Login အောင်မြင်ပြီ!"
  }
  return "❌ Username/Password မှားပြီ"
}