Operators & Control Flow

if / else if / else

const score = 87;

if (score >= 90) {
  console.log("Grade A");
} else if (score >= 75) {
  console.log("Grade B");
} else {
  console.log("Keep practising");
}

Logical operators: && (and), || (or), ! (not). They short-circuit and return the deciding value, not a boolean — the basis of many JS idioms.

The Ternary

const label = score >= 60 ? "pass" : "fail";

Perfect for choosing between two values. Nest them and your reviewer will hunt you down.

Modern Defaults: ?? and ?.

Nullish coalescing ?? — fallback only when null/undefined (unlike ||, which also overrides 0 and “”):

const count = userInput ?? 10;     // 0 stays 0
const countBad = userInput || 10;  // 0 becomes 10 — usually a bug

Optional chaining ?. — safe deep access that yields undefined instead of throwing:

const city = user?.address?.city;          // undefined if any link missing
const first = users?.[0];                  // works with indexes
onSave?.();                                // call only if defined

switch

switch (status) {
  case "draft":
  case "review":              // fall-through groups cases
    showEditor();
    break;                    // forget break = bugs
  case "published":
    showArticle();
    break;
  default:
    show404();
}

Loops

// classic counter
for (let i = 0; i < 5; i++) {
  console.log(i);
}

// for...of — values of any iterable (your default for arrays)
for (const tech of ["js", "css", "react"]) {
  console.log(tech);
}

// for...in — KEYS of an object (not for arrays!)
const user = { name: "Ravi", score: 82 };
for (const key in user) {
  console.log(key, user[key]);
}

// while
let tries = 0;
while (tries < 3) {
  tries++;
}

break exits the loop; continue skips to the next iteration. In practice you’ll often replace loops with array methods (map, filter) — coming up in the arrays topic.