# Trouble with Vector.add
**URL:** https://discourse.processing.org/t/trouble-with-vector-add/24170
**Category:** Coding Questions
**Created:** [September 27, 2020, 7:24pm UTC](https://discourse.processing.org/t/trouble-with-vector-add/24170 "2020-09-27T19:24:21Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@noonscoomo](https://discourse.processing.org/u/noonscoomo)
#### Post date: [September 27, 2020, 7:24pm UTC](https://discourse.processing.org/t/trouble-with-vector-add/24170/1 "2020-09-27T19:24:21Z")
Hi,
I am in trouble with the p5.Vector.add() method and I don’t see why.
My code generates a 2D Vector in setup, adds a random 2D vector in draw, pushes the result in an array and draws the whole array in a loop. If I add the vectors with
v.add(vr);
I get an array with identical vectors in it and nothing works, if I use the static method
v = p5.Vector.add(v,vr);
everything works fine and I don’t understand why.
Here’s the code:
```auto
let v;
let path = [];
function setup() {
createCanvas(600, 600);
v = createVector(200, 200);
}
function draw() {
background(220);
let vr = p5.Vector.random2D();
v.add(vr); // this does not work
//v = p5.Vector.add(v,vr); // this does
path.push(v);
for (i = 0; i < path.length - 1; i++) {
line(path[i].x, path[i].y, path[i+1].x, path[i+1].y);
}
}
```
---
### Author:  [@TheWizardBear](https://discourse.processing.org/u/TheWizardBear)
#### Post date: [September 27, 2020, 7:48pm UTC](https://discourse.processing.org/t/trouble-with-vector-add/24170/2 "2020-09-27T19:48:26Z")
This is down to a little quirk of JavaScript…
When you write `v.add(vr)`, you are adding `vr` to the p5 vector object `v`. This makes intuitive sense.
However, it gets a little confusing when you push `v` into the array `path`. Because of the way JavaScript deals with objects (by reference rather than by value), the `v` you have pushed to the array is not its own new vector as you might expect, but rather it refers to the same object as the `v` that you define at the top of your code. As a result, when you call `v.add(vr)`, you are referring to not only to the `v` you originally defined, but any other `v` that you have used elsewhere.
This means when you add `vr` to `v`, you are adding the vector to all of the vectors in the `path` array, so they all move simultaneously, meaning that when lines are drawn between them, they just appear as a single point.
A simple solution to this (other than using `p5.Vector.add`) is to push `v.copy()` instead of `v`. This uses the p5 vector `copy` method which creates a new identical vector, which does not refer to the original vector object (`v`), meaning that if `v` is changed, this copy will not be.
The reason that `v = p5.Vector.add(v,vr);` does not produce the same problem is that the `v` object is replaced with a new vector object every time you push a vector to the array. This means that `v` no longer refers to the vectors pushed to the array, so changing it does not affect the vectors already in the array.
---
### Author:  [@noonscoomo](https://discourse.processing.org/u/noonscoomo)
#### Post date: [September 27, 2020, 8:03pm UTC](https://discourse.processing.org/t/trouble-with-vector-add/24170/3 "2020-09-27T20:03:07Z")
Hi TheWizardBear,
Thank you so much for that clear explanation. I understand that now, it’s good to know and I think it’s a nice feature to have both options.
---
### Author:  [@KaliBrain](https://discourse.processing.org/u/KaliBrain)
#### Post date: [October 8, 2020, 7:27am UTC](https://discourse.processing.org/t/trouble-with-vector-add/24170/4 "2020-10-08T07:27:40Z")
I didn’t ask the question yet I had a feeling I would learn something valuable. Wasn’t disappointed. Thanks!