Recursive factorial function implementation written in WebAssembly Text (WAT)

factorial.wat

(module
  ;;; Calculates and returns the factorial of the first parameter using
  ;;; recursion.
  ;;; @param  {i32} $x
  ;;;         The value to calculate the factorial of.
  ;;; @return {i32}
  ;;;         The factorial of `$x`.
  (func $fact (param $x i32) (result i32)
    (get_local $x)
    (i32.const 1)

    (if (result i32) (i32.le_s)
      ;; If `$x <= 1` then return `$x`.
      (then
        (get_local $x)
      )
      ;; Else, return `$x * fact($x - 1)`.
      (else
        (get_local $x)
        (i32.const 1)
        (i32.sub)

        (call $fact)
        (get_local $x)
        (i32.mul)
      )
    )
  )
            
  ;; Export the `fact` function so that it can be imported into another script.
  (export "fact" (func $fact))
)