The ajaxComplete seems to work fine for me.
btw, you can test a failed case by disconnecting your wifi before submit.
<script>
$(document).ajaxComplete(function( event, xhr, settings ) {
if(settings.url.includes("https://webflow.com/api/v1/form/")){
const isSuccessful = xhr.status === 200
const redirectFormName = "redirect-form-hehexd"
const isRedirectForm = settings.data.includes(redirectFormName);
console.log(isSuccessful)
console.log(isRedirectForm)
if(isRedirectForm && isSuccessful){
window.location = 'https://discourse.webflow.com/t/successful-form-submission-javascript-event/179645'
}else if(!isRedirectForm){
alert(isSuccessful? "success" : "fail")
}
}
});
</script>