3D Game Programming

Running Code Only If Something Is True

Sometimes we want to skip over code entirely. For these times, we use the if

keyword. Just like while, the if keyword does something with a block of code:

vargame ="started";

// More code here that might change the variable "game"

// to something else...

if(game =="over") {

console.log("Game Over!!!");

}

The if keyword lets us write JavaScript code that runs only if some condition

is true. In this case, we check if game is equal to the string over, using the

double equals (==) operator to do so.

We can also extend an if statement with else if and else. Consider the following

code, which we’ll use to turn and move a raft in Chapter 20, Project: River

Rafting, on page 185:

document.addEventListener("keydown",function(event) {

varcode = event.keyCode;

❶ if(code == 32) pushRaft(); // space

❷ else if(code == 37) rotateRaft(-1);// left

❸ else if(code == 39) rotateRaft(1); // right

❹ else{// Something else

console.log(code);

}

});

We’ll talk more about the code in the project chapters, but we see that

❶if the code is a space bar code, then we push the raft forward

❷otherwise, if the code is for the left arrow key, then we turn the raft to the

left

❸otherwise, if the code is for the right arrow key, then we turn to the right

❹otherwise, some strange key is pressed and we just log the code to the

JavaScript console

Don’t Overuse Ifs

If, else if, and else are very powerful, but can be used too much. We’ll

talk about better approaches in some of the project chapters.

Chapter 7. A Closer Look at JavaScript Fundamentals • 76

Prepared exclusively for Michael Powell report erratum • discuss