if...else
The if statement executes a statement if the last item on the stack is true (non-zero). If the condition is false (0), another statement can be executed.
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
i32.const 0 ;; change to positive number (true) if you want to run the if block
(if
(then
i32.const 1
call $log ;; should log '1'
)
(else
i32.const 0
call $log ;; should log '0'
)
)
)
(start 1) ;; run the first function automatically
)
const url = "{%wasm-url%}";
await WebAssembly.instantiateStreaming(fetch(url), { console });
Syntax
wat
i32.const 0
(if
(then
;; do something
)
(else
;; do something else
)
)
To leave return values on the stack, add the result statement.
wat
i32.const 0
(if (result i32)
(then
;; do something
(i32.const 1)
)
(else
;; do something else
(i32.const 2)
)
)
(drop)
| Instruction | Binary opcode |
|---|---|
if |
0x04 |
else |
0x05 |