StringAdd

• Action Code: 0x21
• Stack: 2 → 1
• SWF version: 4

Implements the legacy string concatenation.

In SWF 4, it corresponded to the operator &.

In SWF 5, it corresponds to the operator add, since the semantics of & were changed to be the ECMA Script bitwise and operator.

The arguments are converted to strings using the same function as the Trace action. In particular, undefined is converted to the empty string "".

Abstract AS2

@t0 = @pop();
@push(@pop() add @t0);

Adobe documentation

ActionStringAdd

ActionStringAdd concatenates two strings.

Field	Type	Comment
ActionStringAdd	ACTIONRECORDHEADER	ActionCode = 0x21

ActionStringAdd does the following:

1. Pops value A off the stack.
2. Pops value B off the stack.
3. Pushes the concatenation BA to the stack.