3.5 Relational and Logical Operators

Programs do not only run statements in order. They often need to check whether a condition is true, then choose what to do next. A condition usually produces a Boolean value: true or false.

Relational operators

Relational operators compare two values. The result of a comparison is a Boolean value.

Common JavaScript relational operators:

• <: less than
• >: greater than
• <=: less than or equal to
• >=: greater than or equal to
• ===: strictly equal to
• !==: not strictly equal to

Important: one equals sign = means assignment. Three equals signs === mean strict comparison.

let age = 17;

console.log(age < 18);       // true
console.log(age === 18);     // false
console.log(age !== 18);     // true

age = 17 stores 17 in the variable age. age === 18 checks whether the current value of age equals 18 and has the same type.

Why === matters in JavaScript

JavaScript also has ==, called loose equality. It may convert types before comparing, which can surprise beginners.

console.log(1 == "1");    // true
console.log(1 === "1");   // false

Use === and !== by default. They are more predictable because they compare both value and type.

Logical operators

Logical operators combine multiple conditions. Their result is still a Boolean value.

• &&: the whole expression is true only when every condition is true.
• ||: the whole expression is true when at least one condition is true.
• !: turns true into false, and false into true.

let age = 20;
let hasTicket = true;

console.log(age >= 18 && hasTicket);    // true
console.log(age < 18 || hasTicket);     // true
console.log(!hasTicket);                // false

It helps to read conditions like plain language: age >= 18 && hasTicket means "the age is at least 18, and the person has a ticket."

Combining conditions

When a condition becomes complex, use parentheses or meaningful variable names to keep the logic readable.

let score = 85;
let attendance = 92;

let passed = score >= 60 && attendance >= 80;
let excellent = score >= 90 || attendance >= 95;

console.log(passed);       // true
console.log(excellent);    // false

Do not rush to squeeze every condition into one line. Naming smaller conditions makes the program easier to read and debug.