Basics
if-else & switch
Decision Making
💡 if-else ek fork wali road hai, switch ek vending machine hai — number dabao, sahi slot khulta hai, bina lambi if-else chain ke.
if, else if, else C/Java jaise hi hain. Ternary operator (condition ? valueIfTrue : valueIfFalse) concise one-liner conditionals ke liye. switch multiple discrete values compare karne ke liye, break zaroori hai warna "fall through" ho jaata hai next case mein.
let marks = 85;
if (marks >= 90) {
console.log("A grade");
} else if (marks >= 75) {
console.log("B grade"); // ye chalega
} else {
console.log("C grade");
}
const grade = marks >= 75 ? "Pass" : "Fail"; // ternary
switch (marks) {
case 100:
console.log("Perfect!");
break;
default:
console.log("Keep trying");
}🔀
if-else ek fork wali road hai, switch ek vending machine hai — number dabao, sahi slot khulta hai, bina lambi if-else chain ke.
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⚡ झट से Recap
- if-else-if chain, ternary (? :) concise conditionals ke liye
- switch = discrete value matching, break zaroori
- Truthy/falsy: 0, "", null, undefined, NaN, false hi falsy hain
इस page में (2 subtopics)
Deeply nested if-else ke bajaye, "guard clauses" (invalid cases ko function ke START mein hi return/handle karo) code ko flatter aur readable banata hai.
// Nested (harder to read):
function processUser(user) {
if (user) {
if (user.isActive) {
return "Processing " + user.name;
}
}
return "Invalid user";
}
// Guard clauses (cleaner):
function processUserClean(user) {
if (!user) return "Invalid user";
if (!user.isActive) return "Invalid user";
return "Processing " + user.name;
}Tip: Guard clauses ek widely-recommended pattern hai clean code likhne ke liye — "unhappy paths" ko jaldi handle karo aur return kar do, main logic ko deeply nested na rakho.
&& ko sirf boolean logic ke liye nahi, CONDITIONAL EXECUTION ke liye bhi use kiya jaata hai — condition && doSomething() sirf tab doSomething() chalata hai jab condition truthy ho.
const isLoggedIn = true;
isLoggedIn && console.log("Welcome back!");
// Agar isLoggedIn false hota, console.log kabhi nahi chalta
// React jaisi libraries mein bahut common pattern:
// {isLoggedIn && <WelcomeMessage />}Tip: Ye pattern especially React/JSX code mein bahut common hai — conditional rendering ke liye if-else ki jagah short-circuit && use hota hai, concise syntax ke liye.