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Form-napper npm version

Hijack a form submit, inject data, resume.

Form Napper provides the ability to interrupt a submit flow and perform an asynchronous task (such as Credit Card tokenization) and inject the results into your form before continuing.


<form id="my-form">
  <label for="card-number">Card Number</label>
  <input type="text" name="card-number" />

  <label for="cvv">CVV</label>
  <input type="text" name="cvv" />

  <input type="submit" />
var form = new FormNapper('my-form');

form.hijack(function (event) {
  console.log('This form\'s submit has been hijacked.');

form.inject('ransomNote', 'Send ransom to...');



FormNapper(String|Element): FormNapper

The FormNapper constructor accepts a single argument as an id string or a DOM element.

Argument Type Description
id String A reference to the id of your form element
element HTMLFormElement A reference to the form element itself

hijack(callback: Function)

The hijack method accepts a callback function that will provide an event object as an argument. This is the browser Event that accompanies the final submit attempt.

inject(name: String, value: String): HTMLInputElement

The inject method will inject a hidden input element into your form and accepts two arguments representing the name and value of that input.

If an input with the provided name is found, its value will be updated with the new value passed to inject.

Whether Form Napper creates the input inside of inject or a previous element existed, that reference will be returned from inject.

Argument Type Description
name String This will be written as the name attribute on the input element
value String This will be the corresponding value to the provided name.


Calling submit will forcefully submit your form and bypass any attached event handlers.


The detach method removes the event listener added in hijack.


We use nvm for managing our node versions, but you do not have to. Replace any nvm references with the tool of your choice below.

nvm install
npm install

All testing dependencies will be installed upon npm install. Run the test suite with npm test.