# Velocitr, velocity and drag helper

4th Jan 2013

I needed a way of applying velocity and drag to a new UI I am putting together, much like the one I built in to jQuery.kinetic. So I have pulled it out in to a simple reusable object.

I have called it Velocitr and it's source is on Github.

## Usage

```// create an instance var v = new Velocitr(); // set starting point v.move(30, true); // move v.move(50); // get velocity assert(v.velocity).equals(20); // apply drag v.drag = 0.9 // => default v.decelerate() assert(v.velocity).equals(18); ```

### Chaining

```var v = new Velocitr(); v.move(30, true) .move(60) .decelerate(); assert(v.velocity).equals(27); ```

## Tests

It comes with a suite of tests which are written with the help of QUnit and Pavlov and can be found in the `test/` folder.

I have written a few QUnit tests but this is the first time I used Pavlov and I much prefer the syntax.

Here's a little taster.

```pavlov.specify('Velocitr', function(){ describe('velocitr', function(){ it('should cap the velocity', function(){ var v = new Velocitr(); v.set(30); assert(v.velocity).equals(30); v.set(100); assert(v.velocity).equals(40); v.set(-100); assert(v.velocity).equals(-40); }); it('should create positive velocity when moved forward', function(){ var v = new Velocitr(); v.move(30); assert(v.velocity).equals(30); v.move(-30, true); v.move(-10); assert(v.velocity).equals(20); }); it('should be able to chain', function(){ var v = new Velocitr(); v.move(30, true) .move(60) .decelerate(); assert(v.velocity).equals(27); }); }); }); ```

## Enjoy

I thought this might be useful for others wanting a similar functionality.