Language - JavaScript: Difference between revisions

Revision as of 21:10, 9 March 2017

Javascript is a high-level object-oriented programming language ideal for use in web applications.

Introduction

If this is your first time working with a Phidget, we suggest starting with the Getting Started page for your specific device. This can be found in the user guide for your device. That page will walk you through installing drivers and libraries for your operating system, and will then bring you back here to use Javascript specifically.

Javascript is capable of using the complete Phidget22 API, including events. We also provide example code in Javascript for all Phidget objects.

Javascript does not require any special programming environment to write. Just use your favourite text editor to write .html and .js files.

Quick Downloads

List of download links, to be added once files are available

Documentation

Example Code

Libraries and Drivers

Getting Started with Javascript

If you are new to writing code for Phidgets, we recommend starting by running, then modifying existing examples. This will allow you to:

Make sure your libraries are properly linked
Go from source code to a test application as quickly as possible
Ensure your Phidget is hooked up properly

Instructions are divided up by operating system. Choose:

Windows XP / Vista / 7
OS X
Linux (including PhidgetSBC)

Windows

Description of Library Files

Javascript programs depend on the following files, which the installers above put onto your system:

jphidgets22.x.x.x.min.js is the Javascript library for Phidget22. The x's in the filename denote the version of the library.

Visual Studio Code

Javascript can be written in any text editor. If you don't have one yet, Visual Studio Code is recommended because it's free and simple.

Use Our Examples

0000000000000000000000000000what will the customers see when they get the examples?

Write Your Own Code

We'll be using jQuery in these examples. jQuery is a Javascript library that will make it easier for us to access elements on an html page.

Let's start by writing a simple html page that makes a dynamic list of attached Phidgets visible to the user. Create a new folder and put the required library files inside. Then create a new HTML file and fill it with the following code:

<!DOCTYPE html>

<html>
<head>
<title>Javascript Test Program</title>
<script src="jquery-2.1.4.min.js"></script>
<script src="sha256.js"></script>
<script src="jphidgets22.1.0.0.min.js"></script>

<script>

	$(document).ready(function () {
		var conn = new jPhidgets.Connection('ws://' + window.location.host + '/phidgets', { name: window.location.host });

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

		conn.onattach = function(dev) {
			$('#list').append(new Option(dev.name,dev.phid));
		}

		conn.ondetach = function(dev) {
			$("#list option[value='" + dev.phid + "']").remove();
		}
	});

</script>
</head>

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

Pages that employ the use of Javascript are divided into two parts: HTML and Javascript. Code in <script> tags is Javascript, and everything else is HTML. HTML will handle the parts of our program that will be visible to the user, and the Javascript will handle all of the behind-the-scenes processing. First, we list all of the Javascript libraries we're including. Next, we have our main script which makes a Phidget connection as soon as the page is ready and loaded. It also sets an attach handler and detach handler which will trigger any time a Phidget is connected or disconnected to the computer. Below this, we have a tiny bit of HTML which will display a select list that our Javascript code will interact with.

Now, in order to test our new program we have to run it on a server.

Setting up the Phidget Network Server

The easiest way to get our code up and running is to host it using the Phidget Network Server. Go to C:\Program Files\Phidgets\Phidget22 and open networkserver.cfg.

000000000000000000000000000 Confirm paths later

Find the [webserver] section and change the docroot to the path of the HTML file you just wrote.

Save, and then run NetworkServer.exe.

Js networkservice.jpg

A window like the one pictured should open.

Running the Program

Now, open a web browser and type localhost:8080 in the address bar. You should see the HTML of the page we just wrote:

<<picture of page>>

Plugging in any Phidget should result in having an entry appear in the list. You will also see any Phidget dictionaries that are running on this network server. Removing the Phidgets should cause them to disappear from the list. You can open the browser's developer console to see the various messages we've been printing out and to set breakpoints in our Javascript code. In Chrome, for example, you can open the developer console with F12.

Now, let's change the program so that we can access a specific channel on a Phidget. In this example we'll read the voltage of a VoltageInput channel on the Phidget 1018_2. Insert a new function to run when the Phidget connection is made:

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

Then, define the function just below this one, but still inside the <script> tags.

function readVoltage() {

		var ch = new jPhidgets.VoltageInput();

		ch.onVoltageChange = function (voltage) {
			$('#res').text(this.getVoltage());
		};

		ch.open();
	}

This function sets up a change handler which will update a piece of text every time the voltage changes. It will match to the first VoltageInput object that it finds.

Lastly, add a line in the HTML section that adds an element where we can change the text to match the present voltage value:

<body>
	<label> Attached Phidgets: </label>
	<div>
		<select multiple id="list" style="width: 500px;"></select>
	</div>
	<label> Voltage Input Value: </label> <label id="res"></label>
</body>

Now save your HTML file and refresh your browser. When you plug in a device with a VoltageInput channel, you should see the voltage value constantly update on the page.

If you wanted to open the VoltageInput object on a VINT Hub port, you would have to add the following two lines just before the open() call:

		ch.setHubPort(0); // open hub port 0
		ch.setIsHubPort(true);

OS X

Linux

Edit the Examples

By following the instructions for your operating system and compiler above, you probably now have a working example and want to understand it better so you can change it to do what you want. This teaching section has resources for you to learn from the examples and write your own. Your main reference for writing C# code will be the Phidget22 API Manual.

Example Flow

Template:ExamplePseudocode

Code Snippets

Step One: Initialize and Open

The Open() function opens the software object, but not hardware. So, it is not a guarantee you can use the Phidget immediately.

For example, if we were using an Digital Input as our device, the create and open calls would look like this:

using Phidget22;
using Phidget22.Events;

namespace Program
{
    class Code
    {
        static void Main(string[] args)
        {
            try
            {

                // Declare a DigitalInput object
                DigitalInput device = new DigitalInput();

                // Hook in any event handlers
                // ...

                // Open the device
                device.Open();

            }
            catch (PhidgetException ex) { Console.WriteLine(ex.Description); }
        }
    }
}

Step Two: Wait for Attachment (plugging in) of the Phidget

To use the Phidget, it must be plugged in (attached). We can handle this simply by calling open with a number as a parameter in place of the basic open. This function works for any Phidget. This will block until a connection is made to the Phidget, or the specified timeout is exceeded:

device.Open(5000);

Sometimes, it makes more sense to handle the attachment via an event. This would be in instances where the Phidget is being plugged and unplugged, and you want to handle these incidents. Or, when you want to use event-driven programming because you have a GUI-driven program. In these cases, an event-driven code snippet to handle the attachment might look something like this:

void attachEventHandler(object sender, Phidget22.Events.AttachEventArgs e) {
{
  Phidget attachedDevice = (Phidget)sender;
  int serialNumber = attachedDevice.DeviceSerialNumber;
  string deviceName = attachedDevice.DeviceName;
  Console.WriteLine("Hello Device {0},  Serial Number: {1}!", deviceName, serialNumber.ToString());
}

And the code to set up the event handler within the code opening your device might look like:

//Code for -creating- device here....

device.Attach += attachEventHandler;

//Code for -opening- device here....

Step Three: Do Things with the Phidget

We recommend the use of event driven programming when working with Phidgets. This allows the program to execute other tasks until the Phidget generates a new event. You can hook a custom function into an event trigger like this, using a Digital Input Phidget as an example:

device.StateChange += input_change;

The input_change method is defined as follows:

void input_change(object sender, Phidget22.Events.DigitalInputStateChangeEventArgs e) {
    textBox1.Text = "State: " + e.State;
}

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 line inside the loop would be something like this, after which you could do something with the value:

bool val = device.State;

device.State = true;

Step Four: Close and Delete

At the end of your program, be sure to close your device.

private void Form1_FormClosing(object sender, FormClosingEventArgs e)  {
    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        If device.Attached Then
            device.Close()
        End If
    End Sub
}

@@ Line 109: / Line 109: @@
 Save, and then run NetworkServer.exe.
-<<picture of network server window>>
+[[image:js_networkservice.jpg|link=]]
 A window like the one pictured should open.

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