---
title: After Effects Expressions
subtitle: Animation on steroïds.
lang: en
slug: "after-effects-expressions"
excerpt: Expressions in After Effects have always been blurry for me. I know they exist, I know they're powerful, I know it could save a lot of time and clean complex keyframe filled compositions but… They are hard to learn!
tags: ["Design"]
createdAt: "2019-04-24T09:00:00.000Z"
code: true
---

import AstroImage from "../../../components/AstroImage.astro";
export const basicExpression =
	"https://assets.nardu.in/basic_expression_d81b12f1ac.jpeg";
export const shortcut = "https://assets.nardu.in/shortcut_39cc19d383.jpeg";

## An ever lasting battle

There is very little documentation and the existing one is hard to find or very old. Very often I just don't have the time to dive into expression learning while animating even though it could help the entire project on the long term.
So the last time I had to do a complex animation, **I took the damn time!**

## The begining of the end (of keyframes).

Everyone uses expressions whether they know it or not. Most of the time it's a rather transparent process for the animator. For example: when parenting a property to another one, After Effects creates an expression for us.

<AstroImage
	src={basicExpression}
	width="728"
	height="80"
	alt="Parenting the position of the form to a null creates an expression."
/>

Over the last updates, Adobe has made an effort to make expressions more accessible to everyone. For example, the expression box is now resembling a code editor thanks to code-coloring and auto-completion features. After Effects expression feel like JavaScript with custom functions.

Those custom functions can be called through a menu once you enabled the expressions on a property. It offers organized shortcut and proper syntax to all of AE native functions and a bunch of JavaScript standard ones.

<AstroImage
	src={shortcut}
	width="728"
	height="322"
	alt="Alt + Click the stopwatch to access the shortcuts."
/>

## So I need to learn javascript to do motion design now?

### Why bother?

I know that most animators don't have any kind of development background. However, if Adobe thought it best to let us use expressions, I think we ought to, at least, try.

> A lot of incredible professionals like [Mt Mograph](https://www.mtmograph.com/) and [Video Copilot](https://videocopilot.net/) use expressions.

Like every optimization process, building an expressions knowledge takes time. However, like all optimization process, you will benefit from it afterwards.

### Where to learn

I've gathered a list of my favourite learning grounds. Plenty more exist, **go get'em!**

- [Adobe official expression starter guide (FR)](https://helpx.adobe.com/fr/after-effects/using/expression-language-reference.html)
- [Adobe official expression basic (EN)](https://helpx.adobe.com/after-effects/using/expression-basics.html)
- [Adobe forums for expressions](https://community.adobe.com/t5/after-effects/bd-p/after-effects?page=1&sort=latest_replies&filter=all&topics=label-expressions)
- [Creative Cow expressions forums](https://creativecow.net/forums/forum/adobe-after-effects-expressions/)
- [Youtube channel about expressions](https://www.youtube.com/playlist?list=PLvr5U5ZSt6IzHyvSL9fo0M9NRPsTvra31)
- [All expressions explained](http://aescript.jecool.net/reference/)
- [All expressions explained again](http://expressions.aenhancers.com/index.html)
- [Nice examples of basic expressions](https://www.schoolofmotion.com/tutorials/amazing-expressions-in-after-effects)

## Real world example

### Number counter

Let's say you need to animate a rather simple counter from 0% to 100%.

- Start by creating a text layer. Define your typographic choices, colours, etc.
- On the effect menu add expression options > slider control
- Alt + Click the Source text property

<video width="728" loop controls preload="metadata">
	<source src="https://assets.nardu.in/alt-counter.mp4" type="video/mp4" />
</video>

- Parent the source text to the slider control through the pickwhip.

<video width="462" loop controls preload="metadata">
	<source src="https://assets.nardu.in/pickwhip.mp4" type="video/mp4" />
</video>

You should get something like this in the expressions panel:

```javascript
effect("Slider Control")("Slider")​
```

- Set two keyframes on the slider from 0 to 100. The text should update accordingly.
- By default, After Effects does not round numbers. In the expression panel, wrap your expression with the `Math.round()` function.

<video width="728" loop controls preload="metadata">
	<source src="https://assets.nardu.in/round.mp4" type="video/mp4" />
</video>

```javascript
Math.round(effect("Slider Control")("Slider"))​
```

Great! We have a working counter. But we wanted a percentage counter. We could add a % glyph in another text layer but let's not.

Still in the expression panel, we're going to add a string containing the % glyph, using basic JavaScript concatenation: `+ '%'`

```javascript
Math.round(effect("Slider Control")("Slider")) + '%'​
```

<video width="538" loop controls preload="metadata">
	<source src="https://assets.nardu.in/percent.mp4" type="video/mp4" />
</video>

**And there we go!** A fully functioning and customizable counter using a slider controller and expressions.