Learn Logical Operators

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When you need to make decisions in your code based on more than one condition, logical operators let you combine or modify these conditions. JavaScript gives you three main logical operators: AND (&&), OR (||), and NOT (!).
These operators are used to join multiple boolean expressions or to invert their values.

The AND operator (&&) returns true only if both conditions are true;
The OR operator (||) returns true if at least one of the conditions is true;
The NOT operator (!) flips the value of a condition: if a condition is true, ! makes it false, and vice versa.

You use these operators most often in if statements to control the flow of your program based on more complex logic.


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const age = 20;
const hasTicket = true;

// Using AND (&&): both conditions must be true
if (age >= 18 && hasTicket) {
  console.log("You can enter the event.");
} else {
  console.log("Entry denied.");
}

// Using OR (||): at least one condition must be true
const isMember = false;
if (age >= 18 || isMember) {
  console.log("You qualify for a discount.");
}

// Using NOT (!): invert a condition
const isBanned = false;
if (!isBanned) {
  console.log("Access granted.");
}

When you combine logical operators, operator precedence determines the order in which they are evaluated. In JavaScript, the NOT (!) operator has the highest precedence, followed by AND (&&), and then OR (||).

This means expressions with ! are evaluated first, then &&, and finally ||. You can use parentheses () to group conditions and control the evaluation order.

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Section 1. Chapter 8

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Section 1. Chapter 8