Boolean Expressions

Overview

Boolean expressions are logical statements that evaluate to either true or false.

They are one of the most fundamental concepts in computer science because they allow programs to make decisions and control behavior dynamically.

In programming, boolean expressions are used everywhere, including:

  • Conditional statements - Game logic - Collision detection - User authentication - AI behavior - Input validation - Loops - Error checking

In AstroPlatformer, boolean expressions help determine whether systems are available and whether certain actions should occur.

The game uses logical checks to safely control gameplay systems and avoid runtime errors.

What is a Boolean?

A boolean is a data type that can only have two values:

true
false

Examples:


const gameRunning = true; const playerDead = false;

Booleans are commonly used to represent states or conditions inside a program.

What is a Boolean Expression?

A boolean expression is any expression that evaluates to either true or false.

Example:

5 > 3

This evaluates to:

true

Another example:


10 === 20

This evaluates to:

false

Programs use these expressions to decide what code should run.

Comparison Operators

Boolean expressions often use comparison operators.

Common operators include:

Operator Meaning   — —   === Equal to   !== Not equal to   > Greater than   < Less than   >= Greater than or equal   <= Less than or equal

Examples:

score > 100


lives === 0

playerHealth <= 0

Each expression evaluates to either true or false.

Conditional Statements

Boolean expressions are commonly used with if statements.

Example:

const score = 150;

if (score > 100) {
  console.log('High score reached!');
}

The code inside the block only runs if the boolean expression is true.

Logical Operators

Programs often combine multiple boolean expressions together.

Common logical operators include:

Operator Meaning   — —   && AND   || OR   ! NOT

Using && (AND)

The && operator requires both conditions to be true.

Example:


if (playerAlive && levelComplete) { console.log('Advance to next level'); }

Both conditions must be true for the code to execute.

Using || (OR)

The || operator requires only one condition to be true.

Example:

if (hasKey || doorUnlocked) {
  console.log('Door can open');
}

Only one condition needs to be true.

Using ! (NOT)

The ! operator reverses a boolean value.

Example:

const paused = false;

if (!paused) {
  console.log('Game is running');
}

Because paused is false, !paused becomes true.

AstroPlatformer Example

The following code comes directly from AstroPlatformer:


if (sm && typeof sm.updateScoreDisplay === 'function') { sm.updateScoreDisplay(gameEnv.stats.coinsCollected); }

This snippet uses a boolean expression to safely verify that the score manager exists before updating the display.

This prevents errors if the score manager has not initialized properly.

Breaking Down the Expression

The expression contains two separate conditions:

sm

and

typeof sm.updateScoreDisplay === 'function'

These are combined using the && operator.

Condition 1: Checking if sm Exists


sm

This checks whether the score manager object exists.

If sm is:

  • null - undefined - false

then the condition fails.

This protects the program from accessing missing objects.

Condition 2: Checking the Function Type

typeof sm.updateScoreDisplay === 'function'

This verifies that updateScoreDisplay is actually a function before calling it.

Without this check, the program could throw an error such as:

TypeError: sm.updateScoreDisplay is not a function

This is an example of defensive programming.

Why Boolean Expressions Matter in Games

Games constantly evaluate conditions using boolean logic.

Examples include:

  • Is the player alive? - Has the level been completed? - Is the enemy nearby? - Did the player collect the item? - Is the game paused? - Has the timer expired?

Without boolean expressions, games could not react dynamically to player actions.

Collision Detection Example

Boolean expressions are heavily used in collision systems.

Example:


if (player.x < enemy.x + enemy.width && player.x + player.width > enemy.x) { console.log('Collision detected'); }

This determines whether two objects overlap.

Collision systems are built almost entirely from boolean logic.

Boolean Variables

Programs often store conditions inside variables.

Example:

const playerDead = health <= 0;

if (playerDead) {
  endGame();
}

This improves readability and organization.

Truthy and Falsy Values

JavaScript also supports truthy and falsy values.

Falsy values include:

  • false - 0 - null - undefined - '' - NaN

Everything else is generally considered truthy.

Example:

if (username) {
  console.log('Username exists');
}

This checks whether username contains a value.

Nested Boolean Logic

Programs can combine many boolean expressions together.

Example:


if (playerAlive && hasWeapon && ammo > 0) { shoot(); }

This creates more advanced game logic.

Boolean Expressions in Loops

Loops also use boolean expressions.

Example:

while (health > 0) {
  updateGame();
}

The loop continues while the condition remains true.

Defensive Programming

Boolean expressions are extremely important for defensive programming.

Defensive programming means writing code that safely handles unexpected situations.

Example:

if (player && player.inventory) {
  console.log(player.inventory);
}

This prevents errors caused by missing objects.

AstroPlatformer uses similar boolean checks to safely handle game systems.

Real-World Uses of Boolean Logic

Boolean expressions appear throughout modern software.

Examples include:

System Boolean Check   — —   Login Systems Is password correct?   Games Is player alive?
  Websites Is user authenticated?   APIs Was request successful?
  AI Systems Is target visible?   Navigation Apps Has destination been reached?

Boolean logic is one of the foundations of programming.

Why Boolean Expressions Matter in AstroPlatformer

AstroPlatformer uses boolean expressions to safely manage systems such as:

  • Score managers - Leaderboards - Player states - Collision systems - Game events - Rendering logic - Level progression

The boolean checks help the game:

  • Prevent crashes - Verify objects exist - Control gameplay flow - Handle missing systems safely - Improve overall stability

Without boolean logic, the game would not be able to make intelligent decisions dynamically.

Key Takeaways

  • Boolean expressions evaluate to true or false - Boolean logic controls program decisions - Comparison operators create conditions - Logical operators combine conditions - && means AND - || means OR - ! means NOT - Boolean expressions are essential for games - AstroPlatformer uses boolean checks for safe system handling

Boolean expressions are one of the most important building blocks of programming and game development.

Quick Example


if (player.health <= 0) { endGame(); }

Summary

Covers boolean expressions and logical operators used to evaluate conditions, combine checks, and build defensive game logic.