Web-Embed API

Embed your flows within other webpages, with communication between the embed and the parent page
The Formsort Github repository can be found at @formsort/web-embed-api.
If you're using React, see @formsort/react-embed which is a handy wrapper around the web-embed-api.
Once you are finished writing your web-embed-api code, check out our Setting up a dev environment doc to begin testing the embed in your webpage.


First, install:
# yarn add @formsort/web-embed-api
# npm install @formsort/web-embed-api --save
Then, initialize the embed and load a flow.


FormsortWebEmbed(rootEl: HTMLElement, config?: IFormsortWebEmbedConfig)
Initializes a Formsort iframe as a child of the rootEl provided.
const embed = FormsortWebEmbed(document.body);
The optional config object has the following interface:
interface IFormsortWebEmbedConfig {
useHistoryAPI?: boolean; // Default: false
autoHeight?: boolean; // Default: false
style?: {
width?: CSSStyleDeclaration['width'];
height?: CSSStyleDeclaration['height'];
authentication?: {
idToken?: string; // ID Token for authenticated flows
config properties
  • useHistoryAPI: When redirecting, should we use the HTML5 History API (namely, window.pushState), or just change the URL in its entirety?
    Helpful if you have a single-page app and want to change the container's URL without reloading the entire page. Note that you'll have to listen to the popstate event on the embedding window to detect this navigation.
  • autoHeight: Should the embedding <iframe> resize so that it matches the content of the currently loaded flow?
  • style: CSS properties to be applied to the iframe container.
  • authentication.idToken: When the Flow requires an ID token, this can be used to provide it.
loadFlow(clientLabel: string, flowLabel: string, variantLabel?: string, queryParams?: Array<[string, string]>) => void
// Ex (w/o query parameters):
embed.loadFlow('formsort', 'onboarding', 'main');
// Ex (w/ query parameters):
embed.loadFlow('formsort', 'onboarding', 'main', ['utm_medium','social']);
Starts loading a Formsort variant, or a flow.
Note that variantLabel is optional. If it is not provided, a variant will be chosen from the flow:
  • Based on weights (e.g. variant split testing), if weights are assigned
  • At random, if no weights are assigned
unloadFlow() => void
Remove inserted iFrame and all its event listeners.

setSize(width: number, height: number) => void

Set the CSS size of the embed.
You may also style the embed's iframe using CSS - it is the iframe child of the rootEl, so you'd use the selector #rootEl > iframe.

Event listeners

embed.addEventListener(eventName: key of IEventMap, fn: IEventMap[eventName]) => void
If the flow is embedded in a whitelisted domain, each event listener will be passed the user's answers.
The events include:
FlowLoaded (answers?: { [key: string]: any } ) => void
Set a callback function to be called when the Formsort flow has loaded completely.
Note that this is more accurate than listening for the iframe's load event, as this is sent from within the Formsort application code and not merely when the DOM is loaded.
You can listen for this to do things like hide the frame container, or display a loading indicator, until everything is loaded to ensure a seamless initial experience.
// Ex:
const embed = FormsortWebEmbed(document.body);
embed.addEventListener('FlowLoaded', () => {
console.log('Flow has loaded!');
embed.loadFlow('formsort', 'onboarding', 'main');
FlowFinalized (answers?: { [key: string]: any }) => void
Set a callback to be called when the flow is complete, meaning the user has finished all of the steps available to them.
Useful for performing an action after the flow is complete, such as displaying a congratulations or starting a payment process.
FlowClosed (answers?: { [key: string]: any }) => void
Set a callback to be called when the user abandons the flow before finalizing it.
Note that this is only possible if your style set defines a close button.
StepLoaded (answers?: { [key: string]: any }) => void
Set a callback to be called when a new step is loaded.
This will happen once after the flow is loaded, if the user hasn't previously completed the flow. Subsequently, this event will happen following the completion of each step, except for the completion of the final step.
StepCompleted (answers?: { [key: string]: any }) => void
Set a callback to be called when a step is completed. This includes the completion of the final step, before the "FlowFinalized" event.
redirect ({ url: string, answers?: { [key: string]: any } }) => ({ cancel?: boolean }) | undefined
Set a callback to customize the way Formsort handles redirects. To cancel Formsort's handling of the redirect, return:
cancel: true;
If the callback does not return a value, Formsort will handle the redirect as usual.
This is helpful if you're embedding Formsort within a single-page app that has custom URL route handling.
unauthorized () => void
Set a callback for unauthorized Formsort messages.
This callback is used when the Formsort Flow is authenticated but the ID token is missing or invalid.


By default, the web embed accesses the production formsort servers. If you would like to point to another flow server, set origin in the config to the correct base URL, for example:
FormsortWebEmbed(document.body, { origin: 'http://localhost:4040' });