Promote

(module
  (import "console" "log" (func $log (param f64)))
  (func $main

    f32.const 10.5 ;; push an f32 onto the stack

    f64.promote_f32 ;; promote from f32 to f64

    call $log ;; log the result

  )
  (start $main)
)

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

;; push an f32 onto the stack
f32.const 10.5

;; promote from f32 to f64
f64.promote_f32

;; the top item on the stack will now be the value 10.5 of type f64