Rewrite

My first version wasn't usable.
I've rewritten the code to be able to make use of the function.

lib/jack.js

@@ -1,14 +1,31 @@
-"use strict";
+'use strict';
 
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
-exports.preventSubmission = preventSubmission;
-function preventSubmission(submission, callback) {
-  submission.preventDefault();
-  if (callback) {
-    callback();
+exports.default = preventFormSubmission;
+
+
+/**
+ * Sets up a form with an event listener on the submit event that prevents
+ * submission.
+ */
+function preventFormSubmission(formId, callback) {
+  var form = document.getElementById(formId);
+
+  if (form === null) {
+    throw new Error('The form with id ' + formId + ' was not found on the page.');
   } else {
-    return;
+    var submitHandler = function submitHandler(submission) {
+      submission.preventDefault();
+
+      if (callback) {
+        callback();
+      } else {
+        return;
+      }
+    };
+
+    form.addEventListener('submit', submitHandler, { capture: true, passive: false, once: false });
   }
 }

lib/jack.js.flow

@@ -1,10 +1,25 @@
 // @flow
 
-export function preventSubmission(submission: Event, callback?: () => void): void {
-  submission.preventDefault();
-  if (callback) {
-    callback();
+/**
+ * Sets up a form with an event listener on the submit event that prevents
+ * submission.
+ */
+export default function preventFormSubmission(formId: string, callback?: () => void): void {
+  const form = document.getElementById(formId);
+
+  if (form === null) {
+    throw new Error(`The form with id ${formId} was not found on the page.`);
   } else {
-    return;
+    const submitHandler = function(submission: Event) {
+      submission.preventDefault();
+
+      if (callback) {
+        callback();
+      } else {
+        return;
+      }
+    }
+
+  form.addEventListener('submit', submitHandler,  {capture: true, passive: false, once: false });
   }
 }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "customary",
-  "version": "1.0.2",
+  "version": "2.0.0",
   "description": "Prevents form submission after native validation has taken place.",
   "main": "lib/jack.js",
   "scripts": {

src/jack.js

@@ -1,10 +1,25 @@
 // @flow
 
-export function preventSubmission(submission: Event, callback?: () => void): void {
-  submission.preventDefault();
-  if (callback) {
-    callback();
+/**
+ * Sets up a form with an event listener on the submit event that prevents
+ * submission.
+ */
+export default function preventFormSubmission(formId: string, callback?: () => void): void {
+  const form = document.getElementById(formId);
+
+  if (form === null) {
+    throw new Error(`The form with id ${formId} was not found on the page.`);
   } else {
-    return;
+    const submitHandler = function(submission: Event) {
+      submission.preventDefault();
+
+      if (callback) {
+        callback();
+      } else {
+        return;
+      }
+    }
+
+  form.addEventListener('submit', submitHandler,  {capture: true, passive: false, once: false });
   }
 }