Javascript for After EffectsEdit

These are standard and common functions used by After Effects. Although many can be used in an Expressions field, all of these are accessable by running a script manually.

Types of scriptsEdit

There are two basic types of scripts which AE uses, uncompiled and compiled.

Uncompiled JavascriptEdit

An uncompiled Javascriptis the most common script you'll see. These are the scripts have filenames ending in .jsx and can be opened with any text editor and edited, and you can see the javascript code when opened. These scripts are meant to be flexible and available for anyone to edit.

Compiled JavascriptEdit

Compiled scripts work exactly like an uncompiled script only the file is encoded for protection. These types of scripts are meant for commercial distribution and cannot be edited by anyone but the author.


What are they?

You can think of a variable as a box that can store different types things based on the boxes shape.  For example, a number box (variable) can store numbers.  A string box can store a string of numbers and sletters surrounded by quotes "".  Normally we create a box before refering to it.   You wouldn't normally tell someone to give you a plooper unless you told that person what a plooper is.  ex. "A plooper is the number 5.  can you tell me what a plooper is?".  then answer would be, "The number 5"  Establishing the existance of your variable in this manner is called declaration.  You must declare your variable before using it.

Declaring variables

Variables can be declared with a "var" in front of them. ex "var myNumber".  you can also assign a value to your variable at the same time.  "var myNumber = 5"  Until a variable is assign a value (5) it is considered "undefined."  Variable should be uniquely named.  If you accidently try to declare a variable that already exists, it will be treated as a an assignment and assign any new value in the declaration statement to the variable. If the duplicate declaration has no assignment, then nothing happens. If you try to assign a value to a non-existent variable, JavaScript will create the variable for you.


  • When naming your variable, you must use letters, $, and _   ex.  "myPlooper" or "my_Plooper" or "$myPlooper"
  • never use spaces
  • Javascript is case-sensitive, meaning.  "Plooper" is different from "plooper"
  • Try to use camelCase


The life of a variable is based upon the region in which is was declared.  if it was declared inside a funtion, it doesn't exist outside the function.  if it exists inside a loop, is does not exist outside the loop.  Variables declared outside all loops and functions are considered global and exist while the script is being evaluated.

Fore more information

Escape CharactersEdit

Code Char Output
\' ' single quote
\" " double quote
\\ \ backslash
\b backspace
\f form feed
\n new line
\r carriage return
\t tab


Comparison OperatorsEdit

Comparison Operators
Operator Description Example ( x=3 ) Result
== Is equal to ( never use a single = ) x==5 false
=== vcvcv absolutely equal to (this checks variable type too)*





 != Is not equal to x!=4 true
 !== is NOT equal to (this checks variable type too)*





> Is greater than x>5 false
< Is less than x<5 true
>= Is greater than or equal to x>=5 false
<= Is less than or equal to x<=5 true

Logical OperatorsEdit

Logical Operators
Operator Description Example ( x=3 ) Result


and ( x>1 )&&( x-1>1 ) true
|| or ( x==3 ) || ( x="three" ) true
 ! is not  !(x==3) false

Arithmetic OperatorsEdit

Arithmetic Operators
Operator Description Example ( x=3 ) Result
+ Add x = x+2 x = 5
- Subtract x = x-2 x = 1
* Multiply x = x*2 x = 6
/ Divide x = x / 2 x = 1.5
++ Increment by

Increment (by 1) then return

Return then increment (by 1)

x ++ 2

++ x

x ++

x = 5

x = 4

x = 3 (next time it will = 4)

-- Decrement by

Decrement (by 1) then return

Return then decrement (by 1)

x -- 2

-- x

x --

x = 1

x = 2

x = 3 (next time it will = 2)

 % Divide and get remainder (Modulus) x % 2 x = 1

Assignment OperatorsEdit

Assignment Operators
Operator Description Example ( x=3 ) Result
= Assigns a value x = 5 x = 5
+= adds a value x += 5 x = 8
-= subtracts a value x -= 5 x = -2
*= multiplies a value x *= 5 x = 15
/= Divides by a value x /= 5 x = 0.6
 %= Divides and gets remainder of a value (Modulus) x %= 5 x = 3

Event HandlerEdit

The following are NOT supported by AE at this time.



Name Secure Expression Description
alert() yes no Brings up an OK dialog, used to send the user a message.
confirm() yes no Brings up an ok / cancel dialog and returned the value as a boolean.(good for if statements)
Error() yes no Brings up an error dialog.
prompt() yes no Brings up an ok / cancel dialog asking for user input. If no input is entered, the dialog returns false.


Name Secure Expression Description
isNaN() yes yes Checks if a value is Not a Number.
Math.sqrt() yes yes Finds the square root of a number.

String ObjectEdit

new String(string)

  • charAt() Returns an index of a specified character position
  • charCodeAt() Returns the UNICODE value of a specified character at position
  • concat() Joins two or more strings together into one
  • fromCharCode() Converts UNICODE values into characters
  • indexOf() Finds the first occurance of a string or character and returns its index value of its location. If the string is not found 0 is returned.
  • lastIndexOf() Finds the last occurance of a string or character and returns its index value of its location. If the string is not found 0 is returned.
  • match() Searches a string for a substring, then returns any matches
  • replace() Searches a string for a substring, then replaces any matches with a new string
  • search() Searches a string for a substring, then returns the position of any matches
  • slice() Extracts a part of a string and returns a new string
  • split() Creates a substring of a specified string
  • substr() Extracts the characters from a string, beginning at a specified start position, and through the specified number of character
  • substring() Extracts the characters from a string, between two specified indices
  • toLowerCase() Converts a string to lowercase letters
  • toUpperCase() Converts a string to uppercase letters
  • valueOf() Returns the primitive value of a String object

String Object Properties

  • .Constructor - a reference to the function which created the object
  • .Length - returns the number of characters in a string
  • .Prototype - Allows you to add methods and properties to the sring object

Objects and PropertiesEdit

An Object can be a File, project, folder, comp, layer, effect, etc. Each Object has a set of Properties; a file has a name, a layer has potition and rotation. Below are Objects and a few of their possible properties. In After Effects a specific object hierarchy is used. Meaning that objects contain sub-objects as well as properties.

Classic Javascript Objects


  • + Used between to strings to quickly concatinate them together - instead of using the concat() method. You can also add with "+=".
  • ,
  • ?:
  • delete
  • new
  • this is a context dependand object or property. It's connected to whatever is being passed to a function.
  • typeof
  • void


  • try is like an if statement for errors. Everything in a try block will be executed and but if errors occur, catch statements can pick up the error and parse it.
  • throw will send an error out for a catch statement.
  • catch looks for try or thrown errors and reports them.

  • if checks a true / false condition and executed if true.
  • else

  • continue
  • break
  • switch looks up a value like an "if" statement would, but handles multiple results. This is like using a series of elseIf statements.



  • /* */ - Book ends for a multi-line comment


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