Description
Learning Objectives
• Get familiar with jQuery selectors and syntax
• Practice Ajax requests
• Practice basic Google Charting features
Part 1: Simple Charting Application
Download week10-src.zip from Canvas, Start Eclipse, select “open projects from file
system” under file menu, go to the directory you just extracted the content and click
open. In this case, all the necessary node modules are specified in package.json.
Right click it on the project explorer panel, select Run as then npm install.
You can run plot.js as node.js application. Once the server is started, you can
access it from browser with the address:localhost:3000/. This would display a
simple page with two links. If you click the first link “Pie Chart”, a pie chart would
display. If you click the second link, you will get an errormessage.
Part 2: Understand the code
The simple application does not use MVC structure. All server side processing
logics are implemented in plot.js. Open plot.js in Eclipse and inspect the
content. The script sets view and static folder as usual; it also defines two route
methods.
The method mapped toGET / renders the view entry.pug. The method
mapped to GET /data demon- strates a slightly different response handling method. It
does not send a text or render any view, instead it sends back a hard coded json
object using res.json() function. The json object response is meant for client side
script. But you can view it from browser by sending a request to
localhost:3000/data from your browser.
ExpressJS has predefined functions to configure the response in various ways, for a full
list see reference document https://expressjs.com/en/api.html#res.
Now open entry.pug and inspect its content in Eclipse. The body element of
entry.pug contains two anchor links. You may notice that there is no mapping route
method defined for any in plot.js. Both links are meant to be processed by client
side javascript code. The head element of entry.pug contains links to three scripts. The
first two are third party libraries: jQuery and Google Charts loader. The last
one is our own script: main.js
Majority of the processing in this application happens on client side and is implemented in
main.js. Charting related functions and statements in this script are adapted from Google
Charts Tutorials.(https://developers.google.com/chart/interactive/docs/quick_start)
The first statement in this script calls the load() function to load the corechart
package. This statement is required for any web page using Google Charts. Two
global variables: options and data are declared in the next two statements. A
global function drawPie() is declared to draw a pie chart based on the chart data
stored in data variable. The chartdata is stored as javascript object, the nextfew
statements followgoogleCharts tutorial
(https://developers.google.com/chart/interactive/docs/basic_load_libs) to preparethe
DataTable.jQuery’s$.each()functionisusedtoiterateallkeyvaluepairsin the
javascript object. After DataTable is prepared, a pie chart is created on the designed
container element: $(“#myChart”)[0]. This is equivalent to the raw JavaScript
expression document.getElementById(“myChart”). The chart.draw()
statement will update the element with the chart content.
The next statement registers an even handler on the document.ready event:
$(document).ready(function() {
…
}
Inside the event handler, an ajax request $.getJSON(url,data, callback) is
sent to get the chart data from server. This request is similar to $.get() and
$.post() except that it receives JSON data as response. The response is assigned
to the global variable data, so that it is available to all scripts on this page.
It also registers an event handler to the click event of the link “Pie Chart”. The event
handler disables the default action of the link and calls the drawPie() function.
Part 3: Write your own code
Now write your own code to display a bar charts when a user clicks the “Bar Chart”
link. You can find tutorial on bar chart here: https://developers.google.com/chart/
interactive/docs/gallery/columnchart. Note that Google Charts uses different terminologies for vertical and horizontal bar charts.
