Language - JavaScript: Difference between revisions

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== Edit the Examples ==
== Edit the Examples ==
{{WriteCode_Intro|JavaScript|JavaScript}}
{{WriteCode_Intro|JavaScript|JavaScript|Browser}}


=== Step One: Connect===
=== Step One: Connect===

Revision as of 21:11, 26 June 2018

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Getting Started with JavaScript

Welcome to using Phidgets with JavaScript! By using JavaScript, you will have access to the complete Phidget22 API, including events. We also provide example code in JavaScript for all Phidget devices.

Version Change

Note: The Phidgets JavaScript library has been bumped to version 2.x.x following a rewrite. The version 2 API is mostly identical to version 1, but does have some breaking changes. It is highly recommended that any code written against version 1 be updated to version 2, as version 1 is considered unstable.

Phidget Network Server

The JavaScript library requires the Phidget Network Server. Start by configuring the server for your OS:

The Phidget Server includes a built-in Webserver. This must be enabled when using the JavaScript library in browser, but can be left disabled when using the library from Node.js.

The Phidget Server Webserver can be used to serve files - such as the Phidget JavaScript library, or your own projects. By default, it serves the JavaScript control panel files. The main purpose of the Webserver is to support a Websockets connection for the Browser library - because regular sockets cannot be used in Browser. The Node.js library uses raw sockets to connect to the Phidget Server, and so does not require the Webserver or Websockets.

JavaScript Control Panel

The JavaScript control panel is a Browser version of our Phidget control panel. This can be used to view and control all Phidgets attached to a Phidget server. The JavaScript control panel is installed by default on Windows, macOS and PhidgetSBC. You can also download the source here.

Make sure the Phidget Server - Webserver is enabled, and running, then navigate to http://localhost:8989. You will now see a program written with JavaScript/HTML that mimics the Phidget Control Panel. It will show all the Phidgets attached to your machine. By double-clicking on the Phidgets, and example will launch.

Javascript windows controlpanel.png

Browser

Use Our Examples

One of the best ways to start programming with Phidgets is to use our example code as a guide. Our browser examples are available here.

Write Your Own Code

Let's start by writing a simple HTML page that makes a dynamic list of attached Phidgets visible to the user. We will be using the JavaScript library jQuery in these examples. jQuery is not required in order to use Phidgets, however, it will make it easier for us to access elements on an HTML page.

To start, create a new empty folder.

Next, download the latest JavaScript browser library from here and copy the files into the folder.

Next, create a file called index.html and copy the following code into it (Note: if you have a newer jQuery, modify the code below to match your version): 

<!DOCTYPE html>
<html>
<head>
    <title>Phidget Manager</title>
    <script src="jquery-2.1.4.min.js"></script>
    <script src="sha256.min.js"></script>
    <script src="phidget22.min.js"></script>
    <script>
        $(document).ready(function() {
            var conn = new phidget22.Connection(8989, 'localhost');

            conn.connect().then(function() {
                console.log('connected');
            }).catch(function(err) {
                conn.delete();
                alert('failed to connect to server:' + err);
            });

            var man = new phidget22.Manager({
                onDeviceAttach: function(dev) {
                    $('#list').append(new Option(dev.getDeviceName(), dev.getKey()));
                },
                onDeviceDetach: function(dev) {
                    $("#list option[value='" + dev.getKey() + "']").remove();
                }
            });
            man.open();
        });
    </script>
</head>

<body>
    <label> Attached Phidgets: </label>
    <div>
        <select multiple id="list" style="width: 500px; height: 200px"></select>
    </div>
</body>
</html>

This code uses the Phidget Manager to list any Phidget accessible from your computer (either directly via USB or indirectly over the network).

Finally, double click index.html to open it in a browser. You should see something like this:

Javascript windows example.png

Open the developer console to get a better idea what is going on:

Javascript windows devconsole.png

For information about the Node.js examples, keep reading. Otherwise, skip ahead to the edit the examples section located below.

Node.js

Use Our Examples

One of the best ways to start programming with Phidgets is to use our example code as a guide. In order to run the examples, you will need to download and install Node.js.

Now that you have Node.js installed, select an example that will work with your Phidget:

Navigate to the example folder that you previously downloaded, open the command prompt at this location and enter the following command: 

npm update

Javascript windows npmupdate.png

Next, enter the following command to run the example (replacing Accelerometer with your example name): 

node Accelerometer localhost
Javacsript windows nodeexample.png

You should now have the example up and running. When you are ready, the next step is editing the examples.

Edit the Examples

By following the instructions for your operating system and compiler above, you now have working examples and a project that is configured. This teaching section will help you understand how the examples were written so you can start writing your own code.


Remember: your main reference for writing JavaScript code will be the Phidget22 API Manual and the example code.

Step One: Connect

In Javascript, you must first connect to the Phidget server using the Connection object. Have a look at the Connection API for more details: Phidget22 API -> Select JavaScript then select Connection API. 

function main() {
    var conn = new phidget22.Connection(5661, 'localhost');
    conn.connect().then(function () {
        console.log("Connected");
        runCode();
    }).catch(function (err) {
        console.error("Failed to connect", err);
    });
}

Once a connection has been established, it will stay active until it is closed, even across network outages and server restarts.

Multiple Connections can be created and connected at once. Any opened Phidget or Manager objects will match against devices on all connections.

Step Two: Create and Open

After connecting, create a new channel object of the correct channel class, then call the open() function to open the channel. Once it has successfully opened we can interact with it and start receiving data from it. We can also set up event handlers just before opening.

For example, if we were using an Digital Input as our device, it would look like this: 

function runCode() {
    var ch = new phidget22.DigitalInput();

    ch.onAttach = digitalInput_attach;
    ch.onStateChange = digitalInput_change;

    ch.open().then(function () {
        // code to execute after open succeeds
    }).catch(function (err) {
        // code to execute if open fails
    });
}

Once the channel successfully opens, you can access it and you will start to get events from it. We can define the event handler functions : 

function digitalInput_attach(ch) {
    console.log(ch + ' attached');
}

function digitalInput_change(state) {
    console.log('state changed:' + state);
}

Now that they've been registered in the runCode() function and the device has been opened, these event handlers will be able to trigger. The first one triggers when the DigitalInput channel attaches, and the second one will trigger whenever the state of the attached DigitalInput changes.

Step Three: Do Things with the Phidget

Some values can be directly read and set on the Phidget. These functions can be used inside a polling loop as an alternative to event driven programming. The lines inside the loop would be something like this, after which you could do something with the value: 

var di_state = ch.getState(); // get the state of the digital input

Step Four: Close

At the end of your program (or at least, at the end of the part that uses the Phidget), it is advisable to close your device. This ensures that the Phidget will be available to other programs that want to use it, since a channel can only be in use by one program at a time unless it's opened via the Phidget Server. It's not necessary to delete the object after closing in Javascript. 

ch.close();

Further Reading

Phidget Programming Basics - Here you can find the basic concepts to help you get started with making your own programs that use Phidgets.

Data Interval/Change Trigger - Learn about these two properties that control how much data comes in from your sensors.

Using Multiple Phidgets - It can be difficult to figure out how to use more than one Phidget in your program. This page will guide you through the steps.

Polling vs. Events - Your program can gather data in either a polling-driven or event-driven manner. Learn the difference to determine which is best for your application.

Logging, Exceptions, and Errors - Learn about all the tools you can use to debug your program.

Phidget Network Server - Phidgets can be controlled and communicated with over your network- either wirelessly or over ethernet.

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