View source for Language - JavaScript

<metadesc>Communicate with sensors, controllers and relays with Phidgets! Our JavaScript API supports Node.js and Browsers.</metadesc>
[[Category:Language]]
__TOC__

== Quick Downloads ==
=== Documentation ===

*{{Phidget22API}} (Select JavaScript from drop-down menu)

=== Libraries ===

*'''Browser''': [{{SERVER}}/downloads/phidget22/libraries/any/Phidget22JavaScript.zip JavaScript Library Download]
*'''Node.js''': npm install phidget22

=== Example Code ===

*[{{SERVER}}?view=code_samples&lang=JavaScript&os=Nodejs JavaScript Examples (Node.js)]
*[{{SERVER}}?view=code_samples&lang=JavaScript&os=Browser JavaScript Examples (Browser)]

=== Tools ===

*[{{SERVER}}/downloads/phidget22/tools/any/Phidget22JavaScriptControlPanel.zip JavaScript Control Panel Source]

=== OS Libraries ===

{{AllQuickDownloads}}

== Getting Started with JavaScript ==
Welcome to using Phidgets with JavaScript! By using JavaScript, you will have access to the complete {{Phidget22API}}, 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:

* [[OS - Windows#Phidget Network Server|Windows]]
* [[OS - OS X#Phidget Network Server|macOS]]
* [[OS - Linux#Phidget Network Server|Linux]]
* [[OS - Phidget SBC#Phidget Network Server|PhidgetSBC]]

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 [{{SERVER}}/downloads/phidget22/tools/any/Phidget22JavaScriptControlPanel.zip 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.

[[File:Javascript_windows_controlpanel.png|link=|center]]

== 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 [{{SERVER}}?view=code_samples&lang=JavaScript&os=Browser 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 [https://jquery.com/download/ 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 [{{SERVER}}/downloads/phidget22/libraries/any/Phidget22JavaScript.zip 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):

<syntaxhighlight lang=javascript>
<!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>
</syntaxhighlight>

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:
[[File:Javascript_windows_example.png|link=|center]]

Open the developer console to get a better idea what is going on:
[[File:Javascript_windows_devconsole.png|link=|center]] 

For information about the Node.js examples, keep reading. Otherwise, skip ahead to the [[#Edit the Examples | 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 [https://nodejs.org/ Node.js]. 

Now that you have Node.js installed, select an example that will work with your Phidget:
*[{{SERVER}}?view=code_samples&lang=JavaScript&os=Nodejs JavaScript Examples (Node.js)]

Navigate to the example folder that you previously downloaded, open the command prompt at this location and enter the following command:
<syntaxhighlight lang='bash'>
npm update
</syntaxhighlight>

[[File:Javascript_windows_npmupdate.png]]

Next, enter the following command to run the example (replacing Accelerometer with your example name):
<syntaxhighlight lang='bash'>
node Accelerometer localhost
</syntaxhighlight>
[[File:Javacsript_windows_nodeexample.png|link=|center]]
You should now have the example up and running. When you are ready, the next step is [[#Edit the Examples | editing the examples]].

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

=== Step One: Connect===
In Javascript, you must first connect to the Phidget server using the {{Code|Connection}} object. Have a look at the Connection API for more details: {{Phidget22API}} -> Select JavaScript then select Connection API.

<syntaxhighlight lang=javascript>
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);
    });
}
</syntaxhighlight>

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 {{Code|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:

<syntaxhighlight lang=javascript>

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
    });
}

</syntaxhighlight>

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 :

<syntaxhighlight lang=javascript>

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

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

</syntaxhighlight>

Now that they've been registered in the {{Code|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:

<syntaxhighlight lang=javascript>

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

</syntaxhighlight>

=== 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.

<syntaxhighlight lang=javascript>

ch.close();
	
</syntaxhighlight>

== 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.