loop: Wasm text instruction

The loop statement creates a label that can later be branched to with a br. The loop instruction doesn't loop by itself; you need to branch to it to actually create a loop.

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.

Try it

(module
  ;; import the browser console object, you'll need to pass this in from JavaScript
  (import "console" "log" (func $log (param i32)))

  (func
    ;; create a local variable and initialize it to 0
    (local $i i32)

    (loop $my_loop

      ;; add one to $i
      local.get $i
      i32.const 1
      i32.add
      local.set $i

      ;; log the current value of $i
      local.get $i
      call $log

      ;; if $i is less than 10 branch to loop
      local.get $i
      i32.const 10
      i32.lt_s
      br_if $my_loop

    )
  )

  (start 1) ;; run the first function automatically
)

const url = "{%wasm-url%}";
await WebAssembly.instantiateStreaming(fetch(url), { console });

Syntax

wat
;; label the loop so that it can be branched to
(loop $my_loop

  ;; branch to the loop.
  ;; most of the time you'll want to put this in an if statement and only branch on condition,
  ;; otherwise you have an infinite loop.
  br $my_loop

)

Instruction Binary opcode

loop

0x03

Help improve MDN

Was this page helpful to you?

Yes No

Learn how to contribute

This page was last modified on Nov 23, 2025 by MDN contributors.

View this page on GitHub • Report a problem with this content

loop: Wasm text instruction

In this article

Try it

Syntax

Help improve MDN