Populate form with data from different sources with JavaScript

In this article, you can find examples of how to use JavaScript to prefill a form from different sources.

Populate form fields with a query string

If you want to populate a form with data you already have or make a form more personalized, URL query parameters are the best option for that.

You can add query parameters manually or use placeholders(merge tags) to customize URL parameters in any automation platform, such as MailChimp, Power Automate, Zapier, etc. For instance, populate a form fields with the user’s contact details:

Populate fields with a query string

//use URL with parameters, for example:
    var queryString = window.location.search;
    var urlParams = new URLSearchParams(queryString);
    fd.field('FirstName').value = urlParams.get('firstname');
    fd.field('LastName').value = urlParams.get('lastname');
    fd.field('Email').value = urlParams.get('email');

Populate fields from browser’s local storage

You can save data to the browser’s local storage for later use. For example, you can save some values while the user is working with one form and then autofill another form with data from the local storage using the code:

Populate fields from local storage

//store values in local storage
localStorage.setItem('FirstName', fd.field('FirstName').value);
localStorage.setItem('LastName', fd.field('LastName').value);
localStorage.setItem('Email', fd.field('Email').value);

//retrieve values from local storage on form load
fd.rendered(function() {
    var firstName = localStorage.getItem('FirstName');
    var lastName = localStorage.getItem('FirstName');
    var email = localStorage.getItem('Email');
    if (FirstName) {
        fd.field('FirstName').value = firstName;
    if (LastName) {
        fd.field('LastName').value = lastName;
    if (Email) {
        fd.field('Email').value = email;

You can also store all of the form’s data and populate form with same values when it’s opened again, like this:

//save form data before save
    localStorage.setItem('form-data', JSON.stringify(fd.data()));

//populate form data when form opens
    var data = JSON.parse(localStorage.getItem('form-data'));

Populate fields from external API

You can make requests to an external API to retrieve values. You’ll need to make sure that you have the key if it’s needed and that you follow the instructions from the API developers. For instance, you can determine person’s location and IP with ipapi.co:

Populate fields from external API

//make a request when the form opens
    $.getJSON('https://ipapi.co/json/', function (response) {
        fd.field('Location').value = response.city + ', ' + response.region_code + ', ' + response.country_name;
        fd.field('IP').value = response.ip;

Populate form from external data sources

You can populate form fields and controls from any external data source: a web service or a public file.

Populate fields from external data

//Populate Data Table from a public file
async function externalFile() {
    const data = $.get('https://plumsail.com/assets/forms/data/source.json')
    return data;
fd.rendered(function() {
        fd.control('Control1').value = JSON.parse(data)