Create a client side application

Create an HTML file called client_js.html in your project directory. Add the following code, but make sure you paste the JWT you generated for the user in the earlier step in this tutorial in to the USER_JWT constant:

<!DOCTYPE html>
<html lang="en">
  <script src="./node_modules/nexmo-client/dist/nexmoClient.js"></script>
    input, button { font-size: 1rem; }
    #hangup { display:none; }
  <h1>Call Phone from App</h1>
  <label for="phone-number">Your Phone Number:</label>
  <input type="text" name="phone-number" value="" 
    placeholder="i.e. 14155550100" id="phone-number" size="30">
  <button type="button" id="call">Call</button>
  <button type="button" id="hangup">Hang Up</button>
  <div id="status"></div>


    const callButton = document.getElementById("call");
    const hangupButton = document.getElementById("hangup");
    const statusElement = document.getElementById("status");
    new NexmoClient({ debug: true })
      .then(app => {
        callButton.addEventListener("click", event => {
          let destination = document.getElementById("phone-number").value;
          if (destination !== ""){
          } else {
            statusElement.innerText = 'Please enter your phone number.';
        app.on("member:call", (member, call) => {
          hangupButton.addEventListener("click", () => {
        app.on("call:status:changed",(call) => {
          statusElement.innerText = `Call status: ${call.status}`;
          if (call.status === call.CALL_STATUS.STARTED){
   = "none";
   = "inline";
          if (call.status === call.CALL_STATUS.COMPLETED){
   = "inline";
   = "none";

This is your web page that uses the Client SDK to make a voice call to the destination phone via Vonage.

There are several key components to this code:

  1. A UI that allows you to enter a phone number and then click the Call button to make the voice call.
  2. Code that logs the user in (a JWT is used for authentication).
  3. The function to make the call callServer(number), where number is the destination phone number in E.164 format.

Once you enter the phone number and click the Call button you will hear a voice reporting on call status, as per the first NCCO instruction sent back by the webhook server you built in one of the previous steps:

  "action": "talk", 
  "text": "Please wait while we connect you."

Then the call connects and you can answer and be able to have a conversation via the app.