Object Basics¶
Quick Overview of Day
Understanding object properties.
For now, you can think of an object as a container of properties. This will make more sense with an example or two:
let student = {
name: "Aaron",
age: 17
};
console.log(student.name); // "Aaron"
console.log(student.age); // 17
console.log(student.birthday); // undefined
Note
Although you can use . or [] to access properties of an object, the . syntax is preferred.
Another example:
let circle = {
x: 200,
y: 300,
radius: 50
};
ellipse(circle.x, circle.y, circle.radius*2, circle.radius*2);
To update or add a value to an object:
let student = {
name: "Aaron",
age: 17
};
console.log(student.age) // 17
student.age = 18
console.log(student.age) // 18
console.log(student.birthday) // undefined
student.birthday = "Jan 1"
console.log(student.birthday) // "Jan 1"
Objects are passed by reference, not copied (time for a memory drawing on the whiteboard!). Consider:
let student = {
name: "Aaron",
age: 17,
};
let anotherStudent = student;
anotherStudent.name = "Catherine";
console.log(student.name) // Catherine
Notice that this is very different than how a primitive (immutable) data type works. These are copied, not passed by reference:
let number = 42;
let anotherNumber = number;
anotherNumber = number;
console.log(number) // 42
console.log(anotherNumber) // 42
anotherNumber = 15;
console.log(number) // 42
console.log(anotherNumber) // 15
Note
Other than Number, String, and Boolean, everything you use in JavaScript will be an object. In other words, they will all be passed by reference, not copied. Be careful to make a deep copy yourself if you want a separate version of an array, for example.
Class Demo¶
Create a bubble object. It should have x, y, diameter, and color properties. Spawn 20 bubbles in setup, and push() them all into an array (use a spawnBubble() function to create and push a bubble object into the array). Use a for ... of loop inside the draw loop to display each of the bubbles in the array, and move each bubble randomly each frame. Use window.setInterval(spawnBubble, 500) in the setup function to automatically call the spawnBubble function every half second (500 milliseconds).
The demo should look something like this.
Change the bubble motion to use Perlin noise. The resulting demo should now look something like this.