If

[condition] → []

• Action Code: 0x9d
• Stack: 1 → 0
• SWF version: 4

Adobe documentation

ActionIf

ActionIf creates a conditional test and branch.

Field	Type	Comment
ActionIf	ACTIONRECORDHEADER	ActionCode = 0x9D
BranchOffset	SI16	Offset

ActionIf does the following:

1. Pops Condition, a number, off the stack.
2. Converts Condition to a Boolean value.
3. Tests if Condition is true. If Condition is true, BranchOffset bytes are added to the instruction pointer in the execution stream.

Note: When playing a SWF 4 file, Condition is not converted to a Boolean value and is instead compared to 0, not true.

The offset is a signed quantity, enabling branches from –32768 bytes to 32767 bytes. An offset of 0 points to the action directly after the ActionIf action.