(module  ;; Import the browser console object, which you'll need to pass in from JavaScript  (import "console" "log" (func $log (param i32)))  (func    ;; Label each block for easy reference    ;; (they can also be referenced by their index)    (block $outer_block      (block $middle_block        (block $inner_block          ;; Choose which block to break out of based on their order in the br_table          ;; 0 is `$inner_block`, 1 is `$outer_block`, 2 is `$middle_block`          i32.const 0          ;; Create a br_table with three targets          (br_table $inner_block $outer_block $middle_block)          ;; The code will never reach this point since we broke out of the block          unreachable        )        ;; If you jump out of `$inner_block` but stay in `$middle_block`,        ;; 42 will be logged        ;; If you jump out of `$middle_block` also,        ;; by jumping out of either `$middle_block` or `$outer_block`,        ;; this will be skipped        i32.const 42        call $log      )    )  )  (start 1) ;; Run the first function automatically)

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

;; Add true to the top of the stack so that the `if` statement is executed.i32.const 1(if ;; 2  (then    (block ;; 1      (loop ;; 0        ;; Add a variable to the top of the stack        i32.const 2        ;; 0 = jump to `block`; since item 0 in br_table is 1, it jumps up one level        ;; 1 = jump to `if`; since item 1 in br_table is 2, it jumps up two levels        ;; 2 = jump to `loop`; since item 2 in br_table is 0, it doesn't jump any levels (causing an infinite loop)        ;; Create a br_table with the targets        (br_table 1 2 0)      )    )  ))

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This page was last modified on⁨Nov 23, 2025⁩ byMDN contributors.