app/javascript/turbo/fetch_requests.js in turbo-rails-1.3.2 vs app/javascript/turbo/fetch_requests.js in turbo-rails-1.3.3

@@ -1,19 +1,50 @@
 export function encodeMethodIntoRequestBody(event) {
   if (event.target instanceof HTMLFormElement) {
     const { target: form, detail: { fetchOptions } } = event
 
     form.addEventListener("turbo:submit-start", ({ detail: { formSubmission: { submitter } } }) => {
-      const method = (submitter && submitter.formMethod) || (fetchOptions.body && fetchOptions.body.get("_method")) || form.getAttribute("method")
+      const body = isBodyInit(fetchOptions.body) ? fetchOptions.body : new URLSearchParams()
+      const method = determineFetchMethod(submitter, body, form)
 
       if (!/get/i.test(method)) {
         if (/post/i.test(method)) {
-          fetchOptions.body.delete("_method")
+          body.delete("_method")
         } else {
-          fetchOptions.body.set("_method", method)
+          body.set("_method", method)
         }
 
         fetchOptions.method = "post"
       }
     }, { once: true })
   }
+}
+
+function determineFetchMethod(submitter, body, form) {
+  const formMethod = determineFormMethod(submitter)
+  const overrideMethod = body.get("_method")
+  const method = form.getAttribute("method") || "get"
+
+  if (typeof formMethod == "string") {
+    return formMethod
+  } else if (typeof overrideMethod == "string") {
+    return overrideMethod
+  } else {
+    return method
+  }
+}
+
+function determineFormMethod(submitter) {
+  if (submitter instanceof HTMLButtonElement || submitter instanceof HTMLInputElement) {
+    if (submitter.hasAttribute("formmethod")) {
+      return submitter.formMethod
+    } else {
+      return null
+    }
+  } else {
+    return null
+  }
+}
+
+function isBodyInit(body) {
+  return body instanceof FormData || body instanceof URLSearchParams
 }