block

block creates a labeled scope. Branching to its label exits the block. It can optionally produce results.

(module
  (func (param $n i32) (result i32)
    (block $out
      (br_if $out (i32.eqz (local.get $n)))
      (return (i32.const 42)))
    (i32.const 0))
)

• Label names are optional — you can also target blocks by relative depth index.
• A block with (result ...) must leave that typed value on the stack on all exits.

Instruction Reference

• Control Flow Instructions — block, loop, if, br, br_if