index.md

---

title: block
slug: WebAssembly/Reference/Control_flow/block

---

{{WebAssemblySidebar}}

The block statement creates a label that can later be branched out of with a br.

The loop statement is the opposite of the block statement, in the sense that while branching to a loop jumps to the beginning of the loop, branching to a block jumps to the end of the block; that is, out of the block.

{{EmbedInteractiveExample("pages/wat/block.html", "tabbed-taller")}}

Syntax

;; label the block so that it can be branched to.
(block $my_block

  ;; branch to the block.
  ;; most of the time you'll want to put this in an if statement and only branch on condition,
  ;; otherwise the following control flow are unreachable.
  br $my_block

  ;; this will never be reached, since the br jumped out of the block already.
  unreachable

)

Instruction	Binary opcode
block	0x02