DOMツリー読み込み完了時にも、submitボタンの有効無効を更新するように変更

app/javascript/agreements.js

@@ -4,15 +4,20 @@ document.addEventListener('DOMContentLoaded', () => {
   )
   const submit = document.querySelector('.js-agreements-submit')
 
-  checkboxes.forEach((element) => {
-    element.addEventListener('click', () => {
-      const isSubmit = checkboxes.every((element) => element.checked)
+  const updateSubmitButtonStateFromCheckbox = () => {
+    const isSubmit = checkboxes.every((element) => element.checked)
+    if (isSubmit) {
+      submit.classList.remove('is-disabled')
+    } else {
+      submit.classList.add('is-disabled')
+    }
+  }
 
-      if (isSubmit) {
-        submit.classList.remove('is-disabled')
-      } else {
-        submit.classList.add('is-disabled')
-      }
+  if (checkboxes.length) {
+    checkboxes.forEach((element) => {
+      element.addEventListener('click', updateSubmitButtonStateFromCheckbox)
     })
-  })
+
+    updateSubmitButtonStateFromCheckbox()
+  }
 })