Create/update lead using Javascript for Intercom?

Question

We would like to create/update a lead in Intercom via Javascript, we can do it through the PHP, but I have no idea how to do the same with Javascript, because we are using Unbounce landing page and when visitor fill out the form we would like send it to Intercom and create the lead for us.

We can use Zapier integration inside the Unbounce but passing the UTM parameters is not allowed, so we want to use the Intercom API/Javascript directly.

Below is the PHP script that we are using to create lead through WP Intercom API

Anyone how to do the same using Javascript? so I can put inside the Unbounce page script manager.

$client = new IntercomClient('xxxxxxxxxxxxx=', null);

try {

    // First check if this already exists
    $leads = $client->leads->getLeads(['email' => $post['email']]);
    foreach ($leads->contacts as $lead) {
        $id = $lead->id;
    }

    if(!$id) {
        $id = '';
    } 

    $client->leads->update([
        "id" => $id,
        "email" => $post['email'],
        "name" => preg_replace("/[^a-zA-Z0-9\s]/", "", ucwords($post['first_name'])),
        "last_request_at" => time(),
        "last_seen_ip" => $_SERVER['REMOTE_ADDR'],
        "utm_campaign" => $post['Utm_campaign], 
        "utm_content" => $post['Utm_content'], 
        "utm_medium" => $post['Utm_medium'], 
        "utm_source" => $post['Utm_source'],
        "utm_term" => $post['Utm_term'],
        'Form Message' => preg_replace("/[^a-zA-Z0-9\s]/", "", $post['description'])]
    ]);

} catch(ClientException $e) {
    $response = $e->getResponse();
    $statusCode = $response->getStatusCode();
    if ($statusCode == '404') {
        // Handle 404 error
        return;
    } else {
        throw $e;
    }
}