# Can't use math functions inside class constructor

**URL:** <https://discourse.processing.org/t/cant-use-math-functions-inside-class-constructor/31251>\
**Category:** Beginners\
**Created:** [July 14, 2021, 2:57pm UTC](https://discourse.processing.org/t/cant-use-math-functions-inside-class-constructor/31251 "2021-07-14T14:57:38Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![seanc4s](https://avatars.discourse-cdn.com/v4/letter/s/e19adc/32.png) [@seanc4s](https://discourse.processing.org/u/seanc4s)\
**Post date:** [July 14, 2021, 2:57pm UTC](https://discourse.processing.org/t/cant-use-math-functions-inside-class-constructor/31251/1 "2021-07-14T14:57:38Z")

</div>

Can’t use math functions inside class constructor, and some other functions like print(“Hi”) for example.  
I don’t mind, but it kinda makes my code look ugly having to use JavaScript Math.random() for example. Which has different behavior too.

---

<div class="post-metadata">

**Author:** ![javagar](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/javagar/32/11434_2.png) [@javagar](https://discourse.processing.org/u/javagar)\
**Post date:** [July 14, 2021, 6:20pm UTC](https://discourse.processing.org/t/cant-use-math-functions-inside-class-constructor/31251/2 "2021-07-14T18:20:39Z")

</div>

The following is modified from the _p5.js Objects \> ex01\_Objects_ example. Note that it successfully calls functions from within the constructor.

```auto
/*
 * @name Objects
 * @description Create a Jitter class, instantiate an object,
 * and move it around the screen. Adapted from Getting Started with
 * Processing by Casey Reas and Ben Fry.
 */

let bug; // Declare object

function setup() {
  createCanvas(710, 400);
  // Create object
  bug = new Jitter();
}

function draw() {
  background(50, 89, 100);
  bug.move();
  bug.display();
}

// Jitter class
class Jitter {
  constructor() {
    this.x = random(width);
    this.y = random(height);
    this.diameter = random(10, 30);
    this.speed = 1;
    / ******@javagar added function calls inside constructor****** /
    print("Hello, I'm your new Jitter!!");
    print("My area is " + PI * pow(this.diameter / 2, 2));
  }

  move() {
    this.x += random(-this.speed, this.speed);
    this.y += random(-this.speed, this.speed);
  }

  display() {
    ellipse(this.x, this.y, this.diameter, this.diameter);
  }
}

```

Output:

```
Hello, I'm your new Jitter!!
My area is 88.54418682503436
```

---

<div class="post-metadata">

**Author:** ![KumuPaul](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/kumupaul/32/13072_2.png) [@KumuPaul](https://discourse.processing.org/u/KumuPaul)\
**Post date:** [July 14, 2021, 7:00pm UTC](https://discourse.processing.org/t/cant-use-math-functions-inside-class-constructor/31251/3 "2021-07-14T19:00:18Z")

</div>

You will encounter issues if you try to use global p5.js function statically before your `setup()` function is called. For example, if the following were at the bottom of the code javagar shared it would not work:

```auto
// After declaring class Jitter
let notGoingToWork = new Jitter();

```

this is because the `Jitter` constructor uses `random`, `width`, and `print` which are not yet declared. Similarly using this functions directly at the top level of your file would not work either:

```auto
let alsoNotGoingToWork = random(10);

```

However if you absolutely must use p5.js functions statically before your `setup()` function is called, some functions can be used directly on `p5.prototype`:

```auto
let thisDoesWork = p5.prototype.random(10);

```

But be aware that that’s not going to work for all functions or properties. Some of them require the p5 instance to have already been created.

---

<div class="post-metadata">

**Author:** ![seanc4s](https://avatars.discourse-cdn.com/v4/letter/s/e19adc/32.png) [@seanc4s](https://discourse.processing.org/u/seanc4s)\
**Post date:** [July 14, 2021, 11:06pm UTC](https://discourse.processing.org/t/cant-use-math-functions-inside-class-constructor/31251/4 "2021-07-14T23:06:53Z")

</div>

Okay, I understand. I can’t just type

let a=new Jitter();  
function setup(){  
…  
}

It should be:  
let a;  
function setup(){  
a=new Jitter();  
}

My bad.

---

<div class="post-metadata">

**Author:** ![seanc4s](https://avatars.discourse-cdn.com/v4/letter/s/e19adc/32.png) [@seanc4s](https://discourse.processing.org/u/seanc4s)\
**Post date:** [July 14, 2021, 11:16pm UTC](https://discourse.processing.org/t/cant-use-math-functions-inside-class-constructor/31251/5 "2021-07-14T23:16:13Z")

</div>

Maybe you can add a warning when people do that thing.