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The FormData API

Historically, getting all of the data from a form into a single object was a bit difficult, but modern techniques make it a lot easier.

The FormData object provides an easy way to serialize form fields into key/value pairs.

I recently wrote about this for Steph Eckles’ amazing 12 Days of Web series, and today, wanted to give you a little preview.

How the FormData API works

You can use the new FormData() constructor to create a new FormData object, passing in the form to serialize as an argument.

For example, let’s imagine you have a form that looks like this.

    <label for="title">Title</label>
    <input type="text" name="title" id="title" value="Go to the beach">

    <label for="body">Body</label>
    <textarea id="body" name="body">Soak up the sun and swim in the ocean.</textarea>

    <input type="hidden" name="userId" value="1">

Important! Form fields must have a name attribute to be included in the object. Otherwise, they’re skipped. The id property doesn’t count.

To create a FormData object, you would pass the form into the new FormData() constructor, like this.

// Get the form
let form = document.querySelector('form');

// Get all field data from the form
// returns a FormData object
let data = new FormData(form);

Looping through FormData values

The FormData object is an iterable.

You can loop through it using a for...of loop. Each entry is an array of key/value pairs.

// logs...
// ["title", "Go to the beach"]
// ["body", "Soak up the sun and swim in the ocean."]
// ["userId", "1"]
for (let entry of data) {

You can also use array destructuring to assign the key and value to their own variables within the for...of loop.

// logs "title", "Go to the beach", etc.
for (let [key, value] of data) {

How to get, set, and serialize values (and more!)

In my article on 12 Days, I go into a lot more detail about the nitty-gritty of working with the FormData API. Many thanks to Steph for letting me participate in this year’s series!

Click here to read the whole thing.