JavaScript Documentation
Printing to Console
println(str);
print(str);
// Example:
println("Hello world.");
// Printing without a new line:
print("Hello world. ");
print("How are you?");
Variables
// Declare a variable
var myVarName;
// Initialize a variable
var myVarName = 5;
// Assign to an existing variable
myVarName = 10;
// Print a variable
println(myVarName);
println("The value is: " + myValue);
Functions
// Functions can take in values, called parameters.
// The function below takes in a parameter called
// 'input' and prints it.
function printText(input) {
println(input);
}
// Functions can also return a value.
// The function below takes in a value,
// adds two to it, and returns it.
function addTwo(number) {
return number + 2;
}
// Read a string
var str = readLine(prompt);
// Read an integer
var num = readInt(prompt);
// Read a float
var cost = readFloat(prompt);
// Read a boolean
var bool = readBoolean(prompt);
// You should replace the word prompt with
// the question you'd like to ask. For example:
var name = readLine("What is your name? ");
var age = readInt("What is your age? ");
var finishedWork = readBoolean("Is your work done? ");
Logical Operators
// Logical operators return booleans (true/false values)
x && y // AND operator -- true if BOTH x and y are true
x || y // OR operator -- true if x OR y are true
! x // NOT operator -- true if x is false
// Logical operators in if statements
if(x && y){
println("x and y are both true");
}
if(x || y){
println("x and/or y are true");
}
if(!x && y){
println("x is false and y is true");
}
Comparison Operators
// Comparison operators return booleans (true/false values)
x == y // is x equal to y
x != y // is x not equal to y
x > y // is x greater than y
x >= y // is x greater than or equal to y
x < y // is x less than y
x <= y // is x less than or equal to y
// Comparison operators in if statements
if(x == y){
println("x and y are equal");
}
if(x > 5){
println("x is greater than 5.");
}
Math
// Operators:
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulus (Remainder)
() Parentheses (For order of operations)
// Examples
var z = x + y;
var w = x * y;
// Increment (add one)
x++
// Decrement (subtract one)
x--
// Shortcuts
x = x + y; x += y;
x = x - y; x -= y;
x = x * y; x *= y;
x = x / y; x /= y;
// Modulus
var z = 10 % 4 // 2 * 4 = 8; 10 - 8 = 2
println(z) // prints out: 2
// Absolute value
var abs = Math.abs(x);
// Square root
var sqrt = Math.sqrt(x);
// Rounding
// Math.round() can be used to round numbers
var pi = 3.14;
var roundedPi = Math.round(pi);
println(roundedPi); // prints out: 3
var goldenRatio = 1.618;
var roundedGoldenRatio = Math.round(goldenRatio);
println(roundedGoldenRatio); // prints out: 2
// Floor Division
// Math.floor() can be used to perform floor
// division. With floor division, only the
// integer portion of the quotient is returned.
// For example, 5/2 is 2.5, but with floor division,
// the result is 2 and the .5 is discarded.
var result = Math.floor(5/2);
println(result); // prints out: 2
// Geometry
// Note input is in radians, not degrees
Math.sin(radians); // Returns value between -1 and 1
Math.cos(radians); // Returns value between -1 and 1
Math.tan(radians); // Returns value
Strings
// str.length
// returns the length of a string
// Example
var str = "hello";
var len = str.length; // equals 5
// str.indexOf(search)
// returns the first index of the search
// or -1 if not found. It is case sensitive.
//Examples
var str = "hello";
var pos1 = str.indexOf("l"); // returns 2
var pos2 = str.indexOf("H"); // returns -1
// str.substring(start);
// returns a substring including the
// character at start to the end of the
// string
//Examples
var str = "hello";
var sub1 = str.substring(1); // equals "ello"
var sub2 = str.substring(3); // equals "lo"
// str.substring(start, end);
// returns a substring including the
// character at start, but not including
// the character at end
//Examples
var str = "hello";
var sub1 = str.substring(0,2); // equals "he"
var sub2 = str.substring(1,4); // equals "ell"
Random Numbers
// Random integer between low and high
Randomizer.nextInt(low, high);
Randomizer.nextBoolean();
Randomizer.nextFloat(low, high);
Randomizer.nextColor();
var roll = Randomizer.nextInt(1,6);
var color = Randomizer.nextColor();
Graphics
Canvas
// returns the width of the canvas
getWidth();
// returns the height of the canvas
getHeight();
// Examples
var height = getHeight();
// Returns the x coordinate of the center
// of the canvas
var center = getWidth() / 2;
// Removes all objects from the canvas
removeAll();
All Graphics Objects
// To get the type of the object
var type = obj.getType();
/*
could return:
'Circle'
'Rectangle'
'Text'
'Line'
*/
Circles
// To make a circle
var circle = new Circle(radius);
// To set the location of the center of the circle
circle.setPosition(x, y);
// Example, red circle with 50px radius with center at (100, 200)
var circle = new Circle(50);
circle.setPosition(100, 200);
circle.setColor(Color.red);
// Get the radius
circle.getRadius(); // returns 50
var curRadius = circle.getRadius(); // store in variable
// Change the radius
circle.setRadius(100);
// Get the position of the center of the circle
var x = circle.getX(); // x is 100
var y = circle.getY(); // y is 200
// Change the location of the circle
var x = getWidth() / 2;
var y = getHeight() / 2;
circle.setPosition(x, y); // circle center is in the center of the screen
// Adding to and removing from screen
add(circle); // Add to screen
remove(circle); // Remove from screen
// Move the circle dx horizontally and dy vertically
circle.move(dx, dy);
Rectangles
// To make a rectangle
var rect = new Rectangle(width, height);
// To set location of the upper left corner of rectangle
rect.setPosition(x, y);
// Example, 200x50 blue rectangle with upper left corner at (100, 200)
var rect = new Rectangle(200, 50);
rect.setPosition(100, 200);
rect.setColor(Color.blue);
// Get location of the upper left corner of the rectangle
var x = rect.getX(); // x is 100
var y = rect.getY(); // y is 200
// Change location of the rectangle
var x = getWidth() / 2;
var y = getHeight() / 2;
rect.setPosition(x, y) // upper left corner is at center of screen
// Adding to and removing from screen
add(rect); // Add rectangle
remove(rect); // Remove rectangle
// Move the rect dx horizontally and dy vertically
rect.move(dx, dy);
Arcs
// To make an arc
var myArc = new Arc(radius, start, end, unit);
// More specifically, the parameters are:
// 1. radius of the arc
// 2. starting angle of the arc
// 3. ending angle of the arc
// 4. angle unit (0 for degrees, 1 for radians)
// To set the position of the center of the arc
myArc.setPosition(x, y);
// Example, a 90-degree arc with
// radius of 50 and color of red:
var myArc = new Arc(50, 0, 90, 0);
myArc.setPosition(100, 200);
myArc.setColor(Color.red);
// Get the location of the center of the arc
var x = myArc.getX(); // x is 100
var y = myArc.getY(); // y is 200
// Change the location of the center of the arc
var x = getWidth() / 2;
var y = getHeight() / 2;
myArc.setPosition(x, y); // arc center is at center of screen
// Adding to and removing from screen
add(myArc); // Add arc
remove(myArc); // Remove arc
Lines
// To draw a line from (x1, y1) to (x2, y2)
var line = new Line(x1, y1, x2, y2);
// Set the line color to green
line.setColor(Color.green);
// Set the line width to 10 pixels
line.setLineWidth(10);
// Adding to and removing from screen
add(line);
remove(line);
// Move the line dx horizontally and dy vertically
line.move(dx, dy);
// Change the starting point of the line to (x1, y1)
line.setPosition(x1, y1);
// Change the end point of the line to (x2, y2)
line.setEndpoint(x2, y2);
//Get the starting point of the line
var x = line.getX(); // x has same value as x1
var y = line.getY(); // y has same value as y1
Ovals
// To make an Oval
var oval = new Oval(width, height);
// To set location of the center of the oval
oval.setPosition(x, y);
// Example, 200x50 blue oval with center at (100, 200)
var oval = new Oval(200, 50);
oval.setPosition(100, 200);
oval.setColor(Color.blue);
// Get location of the center of the oval
var x = oval.getX(); // x is 100
var y = oval.getY(); // y is 200
// Change location of the oval
var x = getWidth() / 2;
var y = getHeight() / 2;
oval.setPosition(x, y) // oval's center is at center of screen
// Adding to and removing from screen
add(oval); // Add oval
remove(oval); // Remove oval
// Move the oval dx horizontally and dy vertically
oval.move(dx, dy);
Polygons
// To make a polygon
var polygon = new Polygon();
// To add points to the polygon
polygon.addPoint(x, y);
// Example, 4-sided green polygon
// NOTE: The order in which you add the points determines how the polygon is drawn
var polygon = new Polygon();
polygon.addPoint(20, 20);
polygon.addPoint(10, 50);
polygon.addPoint(100, 80);
polygon.addPoint(60, 10);
polygon.setColor(Color.green);
// Check if polygon contains a point
polygon.containsPoint(x, y); // returns boolean
// Adding to and removing from screen
add(polygon); // Add polygon
remove(polygon); // Remove polygon
// Move the polygon dx horizontally and dy vertically
polygon.move(dx, dy);
Text
// To make a graphical text object
var txt = new Text(label, font);
// To set the position of the lower left corner of the text
txt.setPosition(x, y);
// Example
var txt = new Text("Hello, world!", "30pt Arial");
txt.setPosition(100, 200);
txt.setColor(Color.blue);
// Change what the text says
txt.setText("Goodbye!");
// Get the location of the lower left corner of text
var x = txt.getX(); // x is 100
var y = txt.getY(); // y is 200
// Change the location of the text
var x = getWidth() / 2;
var y = getHeight() / 2;
txt.setPosition(x, y) // text's lower left corner is
// in the center of the screen
// Adding to and removing from screen
add(txt); // Add text
remove(txt); // Remove text
// Move the text dx horizontally and dy vertically
txt.move(dx, dy);
Images
// A web image can be added to the graphics canvas
// as a WebImage. WebImages are created, sized,
// and positioned much like other graphics objects.
// To create a new WebImage, use a URL that links
// directly to the image on the Internet.
// Use the Upload Tab in the editor to upload and create
// a valid URL for your own image.
var copter = new WebImage("https://upload.wikimedia.org/" +
"wikipedia/commons/4/41/" +
"Bell_206L3_%28D-HASA%29.jpg");
copter.setSize(300, 150);
copter.setPosition(getWidth()/4, getHeight()/2);
add(copter); // Adding copter to screen
remove(copter); // Removing copter from screen
// Note that the URL to the image must be directly
// to the image file itself. It should generally end with
// something like .png, .jpg, or another image file type.
Images Hosted on CodeHS
- https://static.codehs.com/img/library/characters/penguin.png
- https://static.codehs.com/img/library/characters/monkey.jpg
- https://static.codehs.com/img/library/characters/leopard.jpg
- https://static.codehs.com/img/library/characters/chameleon.jpg
- https://static.codehs.com/img/library/characters/lizard.jpg
- https://static.codehs.com/img/library/characters/butterfly.jpg
- https://static.codehs.com/img/library/objects/icicle.png
- https://static.codehs.com/img/library/objects/helicopter.png
- https://static.codehs.com/img/library/objects/asteroid.png
- https://static.codehs.com/img/library/objects/soccerBall.png
- https://static.codehs.com/img/library/landscapes/flowers.jpg
Color
// There are many color constants. You can set an objects
// color like
obj.setColor(color);
// Specifically,
obj.setColor(Color.RED);
// List of available colors:
Color.RED
Color.GREEN
Color.BLUE
Color.YELLOW
Color.CYAN
Color.ORANGE
Color.WHITE
Color.BLACK
Color.GRAY
Color.PURPLE
// You can also make your own color by giving a red, green,
// and blue component like
var color = new Color(r, g, b);
// The values are between 0-255 for each component. After making
// a new color, you can use it to set the color of an object.
// For example, to set an existing rectangle called
// rect to be brown:
var brown = new Color(139, 69, 19);
rect.setColor(brown);
// Another way to set the color of an object is to use a
// string with the hexadecimal color value with setColor.
// For example, to set a rect object to be pink:
rect.setColor("#FF66CC");
// Other fun functions
// Return a random color
var color = Color.randomRed();
var color = Color.randomGreen();
var color = Color.randomBlue();
// Get a random color from the randomizer
var color = Randomizer.nextColor();
Rotation
/**
* The following graphic objects can be rotated:
* - Rectangle
* - Arc
* - Line
* - Oval
* - Text
* - WebImage
*/
// Set the rotation of the rectangle with these parameters:
// 1. angle to rotate
// 2. angle unit (0 for degrees, 1 for radians)
// This will default to degrees.
rect.setRotation(45, 0); // Sets rotation of the rectangle to 45 degrees
rect.setRotation(45); // Does the same thing.
rect.setRotation(Math.PI / 2, 1); // Sets rotation of the rectangle to Math.PI/2 radians
// Add rotation with these parameters:
// 1. angle to rotate
// 2. angle unit (0 for degrees, 1 for radians)
// This will default to degrees.
rect.rotate(45, 0); // Rotates the rectangle by 45 degrees
rect.rotate(45); // Does the same thing.
rect.rotate(Math.PI / 2, 1); // Rotates the rectangle by Math.PI/2 radians
Booleans
// A boolean is either true or false
var myBoolean = true;
var anotherBoolean = false;
var result = readBoolean("Question? ");
// Not Operator
var x = !y; // x gets the opposite of y
// And Operator
var andExp = x && y;
// Or Operator
var orExp = x || y;
// You can combine many booleans!
var boolExp = x && (y || z);
If Statements, If/Else, If/Else If/Else
if(BOOLEAN_EXPRESSION){
// code to execute if true
}
if(BOOLEAN_EXPRESSION){
// code if true
} else {
// code if false
}
if(x < 0){
println("x is negative.");
}
if(color == "red" || color == "blue" || color == "yellow"){
println("Primary color.");
} else {
println("Not a primary color.");
}
// You can use else if if you have multiple
// conditions, but only one should happen.
if(condition_1){
} else if(condition_2) {
} else if(condition_3) {
} else {
}
// You can always write these using nested
// if/else. For example:
if(condition_1){
// code here runs if condition 1 is true
} else {
if(condition_2){
// if condition 2 is true
} else {
// and here if condition 2 is false
}
}
For Loops
var COUNT = 5;
for(var i = 0; i < COUNT; i++){
/* Repeat code betweeen the brackets 5 times,
* as the COUNT variable is 5. */
}
// Print numbers 0-9
for(var i = 0; i < 10; i++){
println(i);
}
While Loops
while(boolean expression){
/* Repeat code betweeen brackets while
* 'boolean expression' is true */
}
// Countdown from from 15 to 10
var i = 15;
while(i > 10){
println(i);
i--;
}
// This is a loop and a half format
while(true){
// code
if(condition){
break;
}
}
Timers
setTimer(fn, delay); // Create a timer
stopTimer(fn); // Stop a timer
// Example: call moveBall every 40 milliseconds
function moveBall() {
ball.move(x, y);
}
function start() {
setTimer(moveBall, 40);
}
Mouse Events
// Mouse events are used to create programs
// that respond to users' mouse clicks, drags,
// and movements.
// When the mouse event occurs, the function
// registered with the event will be called. Note
// that you leave out the parentheses () when
// passing the name of the function.
// Here is a list of mouse events that can be used:
mouseMoveMethod(functionToCall); // on mouse movement
mouseClickMethod(functionToCall); // on mouse clicks
mouseDragMethod(functionToCall); // on mouse drags
mouseDownMethod(functionToCall); // mouse button depressed
mouseUpMethod(functionToCall); // mouse button released
// Sample program using mouse events
function start() {
// Set up mouse callbacks
mouseMoveMethod(onMouseMove);
mouseClickMethod(addBall);
mouseDragMethod(updateLine);
}
function onMouseMove(e) {
println("Mouse is at (" +
e.getX() + ", " +
e.getY() + ").");
}
function addBall(e) {
var ball = new Circle(20);
ball.setPosition(e.getX(), e.getY());
add(ball);
}
function updateLine(e) {
line.setEndpoint(e.getX(), e.getY());
}
Keyboard Events
function start() {
// Set up keyboard callbacks
keyDownMethod(keyDown);
keyUpMethod(keyUp);
}
function keyDown(e) {
if (e.keyCode == Keyboard.LEFT) {
ball.move(-5, 0);
}
if(e.keyCode == Keyboard.letter('K')){
println("You pressed K");
}
}
function keyUp(e) {
println("You lifted up a key");
}
Audio Files
// To add a sound file to a program, first create a variable
// to store the sound you want. Be sure to use a link
// directly to the audio file itself (for example,
// if it's an mp3, the link should end with .mp3).
// The link must be a full URL to a sound file that
// is available on the internet.
var mySong = new Audio("link_to_sound_file.mp3");
// To play the file, use .play()
mySong.play();
// To pause a file, use .pause()
mySong.pause();
// To loop a file, first play the file,
// then set .loop to true:
mySong.play()
mySong.loop = true;
Sound
/*
* Create your own sound waves!
*/
// Construct a new Sound with a given note and sound wave type
var sound = new Sound("C4", "square");
var sound2 = new Sound("C1", "sawtooth");
// Set the tone to either a frequency value or a note value
sound.setFrequency(440); // 440 Hz
sound.setFrequency("C4"); // Middle C note
sound.setFrequency("A2"); // Low A note
sound.setFrequency("A#8"); // High A sharp note
/*
* Set the oscillator type for the sound wave. Options are:
*
* Basic waves: "square", "sine", "triangle", or "sawtooth"
* Fat waves: "fatsquare", "fatsine", "fattriangle", or "fatsawtooth"
* AM waves: "amsquare", "amsine", "amtriangle", or "amsawtooth"
* FM waves: "fmsquare", "fmsine", "fmtriangle", or "fmsawtooth"
* Special waves: "pwm", or "pulse"
* Drum sound: "drum"
* Cymbal sound: "metal"
*/
sound.setOscillatorType("sine");
sound.setOscillatorType("square");
// Set the volume (in decibels)
sound.setVolume(2);
/*
* Get information about the sound
*/
var currentVolume = sound.getVolume();
var currentNote = sound.getFrequency();
var currentOscillatorType = sound.getOscillatorType();
/*
* Adding effects to the sound
* Options are: "distortion", "reverb",
* "tremolo", "vibrato", or "chebyshev"
*/
// Add a distortion effect at full capacity
sound.setEffect("distortion", 1);
// Add a tremolo effect at half capacity
sound.setEffect("tremolo", 0.5);
// Add a vibrato effect at 0 capacity
sound.setEffect("vibrato", 0);
/*
* Starting and stopping the sound
*/
// Play the sound continuously
sound.play();
// Play the sound for 3 seconds
sound.playFor(3);
// Stop playing the sound immediately
sound.stop();
Misc
function start() {
mouseClickMethod(turnRed);
}
// If you click on an object, turn it red.
function turnRed(e) {
var elem = getElementAt(e.getX(), e.getY());
if (elem != null) {
elem.setColor(Color.red);
}
}
Arrays
// Create an empty array
var arr = [];
// Create an array with values
var arr = [1, 2, 4];
// An array can have any type
var arr = [4, "hello", x];
// Access an element in an array
var elem = arr[i];
var firstElem = arr[0];
// Set an element in an array
arr[4] = 9;
// Looping over an array
for(var i = 0; i < arr.length; i++){
var cur = arr[i];
// process cur
}
// length of an array
var length = arr.length;
// Add to an array
arr.push(elem);
// Remove last element from array
var last = arr.pop();
// Finding the index of an element in a list
var index = arr.indexOf(5);
// Remove an element from a list at index i
arr.remove(i)
Maps/Objects
// Object literal
var obj = {
name: "Jeremy",
color: "blue"
};
// Objects/Maps have a collection of key, value pairs
// Set a value
obj["Jeremy"] = "123-4567";
// Get a value for a key
var phone = obj["Jeremy"];
// Loop over an object
for(var key in obj){
var val = obj[key];
// process key and val
}
Sets
// Make a new set named "newSet"
var newSet = new Set();
// Add to a set
newSet.add(5);
// Does a set contain a value
newSet.contains(5); // returns a boolean
// Number of elements in the set
var count = newSet.size; // returns an integer
// Make a new set named "setA"
var setA = new Set();
// Add 2 numbers to the set
setA.add(1);
setA.add(2);
// Make a new set named "setB"
var setB = new Set();
// Add 2 numbers to the set
setB.add(2);
setB.add(3);
// Call the intersect function on "setA" and pass in "setB", store the resulting
// set in a new variable named "mutualSet"
var mutualSet = setA.intersect(setB);
Grids
// Create a grid named "newGrid"
var newGrid = new Grid(rows, cols);
// Get a value in a grid
var elem = newGrid.get(row, col);
// Set a value in a grid
newGrid.set(row, col, val);
// Getting dimensions
var rows = newGrid.numRows();
var cols = newGrid.numCols();
// Is a row, col pair inbounds
newGrid.inBounds(row, col);
// Set all values in grid to initial value
newGrid.init(0); // sets all grid values to 0
// Initialze a grid from an array
newGrid.initFromArray([
[6, 3, 2], // 0th row
[2, 5, 1], // 1st row
[4, 3, 9], // 2nd row
[1, 5, 1] // 3rd row
]);
