Work with web form fields in JavaScript

In this article, you can find examples of how to use JavaScript to make your forms more interactive by hiding, disabling, and making fields mandatory based on certain conditions. Find unique properties of certain field types in the fields section.

In order to access fields in JavaScript, you’ll need to use the fd.field() method, which expects a name of a field you want to retrieve. The name of each field on the form is unique. Select a field and copy its name from the Name property:

Copy Name


You should place JavaScript inside fd events like rendered() or beforeSave() to access the fields or controls that you target.

If you just add these scripts on their own or inside the wrong event in the JavaScript editor, they will not have access to the specified fields, or will execute at the wrong time. Read more about different events in the JavaScript framework basics article.

Populate field value

Set the field once the form loads:

fd.rendered(() => {
    fd.field('StartDate').value = new Date();

//you can also populate field values from URL parameters, for example:
fd.rendered(() => {
    var queryString =;
    var urlParams = new URLSearchParams(queryString);
    fd.field('Text1').value = urlParams.get('param1');
    fd.field('Text2').value = urlParams.get('param2');

Set field’s hint with JavaScript

Set the field’s hint once the form loads:

fd.rendered(() => {
    fd.field('Name').placeholder = 'Enter your full name';

Set field’s title with JavaScript

Set the field’s title once the form loads:

fd.rendered(() => {
    fd.field('Name').title = 'Full Name';

Handle field change

Set the field once value of another field changes:

fd.rendered(() => {

    function setPercentComplete() {
        if (fd.field('Status').value == 'Completed') {
            // Setting the Percent Complete to 100
            fd.field('PercentComplete').value = '100';

    // Calling setPercentComplete when Status value changes

    // Calling setPercentComplete on form loading


Disable field

Disable field once specific conditions are meant.

fd.rendered(() => {

    function disablePercent() {
        if (fd.field('Status').value == 'Completed' && fd.field('PercentComplete').value == '100') {
            // Setting field PercentComplete to a disabled state
            fd.field('PercentComplete').disabled = true;
            // Setting field PercentComplete to an editable state
            fd.field('PercentComplete').disabled = false;

    // Calling disablePercent when the PercentComplete value changes

    // Calling disablePercent on form loading


Hide/show field

Hide/show fields once value of another field changes:

fd.rendered(() => {

    function hideOrShowDueDate() {
        if (fd.field('StartDate').value) {
            // Show the Due Date field
            fd.field('DueDate').hidden = false;
        } else {
            // Hide the Due Date field
            fd.field('DueDate').hidden = true;

    // Calling hideOrShowDueDate when the Start Date value changes

    // Calling hideOrShowDueDate on form loading


Clear fields

Clear fields once value of another field changes:

fd.rendered(() => {

    function clearFields() {
        if (fd.field('Status').value == 'Not started') {
            // Clear fields of any value

    // Calling clearFields when the Status value changes


Validate fields

You can add custom validators to a field to ensure that the value meets certain criteria, and trigger validation when the value of the field changes:

fd.rendered(() => {
        name: 'Attachments validator',
        error: 'Do not attach more than 3 files',
        validate: function(value) {
            if (value.length > 3) {
                return false;
            return true;

The field validator function can also be asynchronous:

fd.rendered(() => {
    //field validator
        name: 'MyCustomValidator',
        error: 'This email is already taken, try another one.',
        validate: function(email) {
            return new Promise(resolve => {
                // make a request to an external service to check whether a user with specified email already exists.
                window.setTimeout(() => {
                    resolve(false); // validation failed
                    // resolve(true) if validation passed
                }, 500);

You can validate fields once value of another field changes:

fd.rendered(() => {

    function validateFields() {
        if (fd.field('Status').value === 'Finished') {
            // Make sure that fields have values if set as required, and check for custom validators

    // Calling validateFields when the Status value changes


Require field based on condition

Set field to required state if conditions are meant:

fd.rendered(() => {

    function setDueDateRequired() {
        if (fd.field('StartDate').value) {
            // Set Due Date required
            fd.field('DueDate').required = true;
        } else {
            // Set Due Date as not required if there is no Start Date
            fd.field('DueDate').required = false;

    // Calling setDueDateRequired when the Start Date value changes

    // Calling setDueDateRequired on form loading


Modify fields with Button control

Button, Hyperlink, and Image controls can execute code when on click. Add code to the control’s Click property, and it will be executed when a user clicks the control.

Click property

This can be used for variety of purposes and you don’t need to include JavaScript inside fd events as by the time the button has loaded, other fields have already loaded as well.

Add this code inside the Click property for the Button control to change the Title field value:

fd.field('Title').value = 'Hello, world!'

For the Hyperlink and Image controls, add event.preventDefault() before the rest of the code to prevent the redirection:

//prevent redirection

Populate fields from external API

When the form opens, you can make requests to an external API and retrieve values from the API. 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, but here’s an example of how it can be done with, an API that will help us determine person’s location and IP:

//make a request when the form opens
fd.rendered(() => {
    $.getJSON('', function (response) {
        fd.field('Location').value = + ', ' + response.region_code + ', ' + response.country_name;
        fd.field('IP').value = response.ip;

Populate fields from browser’s local storage

If you want to store some data in the browser’s cache, you can use local storage for that. For example, you can save some values while the user is working with one form, then retrieve them when the user opens up another form, like this:

//store values in local storage like this:
localStorage.setItem('value1', 'Hello, world!');
localStorage.setItem('value2', fd.field('Title').value);

//retrieve values from local storage
fd.rendered(() => {
    var value1 = localStorage.getItem('value1');
    var value2 = localStorage.getItem('value2');
        fd.field('Text1').value = value1;
        fd.field('Text2').value = value2;

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
fd.beforeSave(() => {
    localStorage.setItem('form-data', JSON.stringify(;

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