Operators and conditions

Maths operators

console.log(7 + 2);  // 9
console.log(7 - 2);  // 5
console.log(7 * 2);  // 14
console.log(7 / 2);  // 3.5
console.log(7 % 2);  // 1   (remainder)
console.log(2 ** 3); // 8   (power)

Comparisons

A comparison gives a boolean. Use === (strictly equal) and !== (not equal). They compare both the value and the type. The older == converts types first, so 5 == "5" is true, which hides bugs. Always use ===.

console.log(5 === 5);   // true
console.log(5 === '5'); // false (number vs string)
console.log(10 > 3);    // true
console.log(18 >= 18);  // true

Making decisions with if

function grade(marks) {
  if (marks >= 90) {
    return 'A';
  } else if (marks >= 75) {
    return 'B';
  } else if (marks >= 35) {
    return 'C';
  } else {
    return 'Fail';
  }
}
console.log(grade(82)); // 'B'

Logic: and, or, not

• a && b is true only when both are true (has ticket AND has ID).
• a || b is true when at least one is true (paid by UPI OR card).
• !a flips true and false (!isLoggedIn means "not logged in").

Truthy and falsy

In a condition, JavaScript treats some values as false: false, 0, "" (empty string), null, undefined and NaN. These are called falsy. Everything else is truthy, even "0" and an empty list [].

Short forms

const age = 20;
const label = age >= 18 ? 'adult' : 'minor'; // ternary: condition ? yes : no

const userCity = null;
const city = userCity ?? 'Not given';        // ?? gives a default for null/undefined
console.log(label, city); // adult Not given

A switch statement compares one value against many fixed cases. It is handy for things like a menu choice, but a chain of if / else if is fine for most checks.