Title of the document

Review

Last day we saw how we can add a JavaScript program to a web page: we use the HTML element <script>, with its companion closing tag </script>. Inside those two tags we write our program!

Our first program consisted in printing some text on the body of the page when using the htmlLiveEditor. The first message we printed was Hello World!.

But, in order to build a web app like Facebook, Google Maps or Gmail, we need more than just printing a string of characters. Indeed, a computer program consists in much more than simply printing something on the screen!

Today

Today we have seen one new key concept: a variable. In computer science, a variable consists of two things, a label and a value... Well, I'm lying a bit. Actually, it consists of three things, a label, a value and a memory location.

The label myName is actually just an address. It points to the memory address of the start of the data we store there ('J').

Code:

Defining a variable: var myName = "John" ;

Computer Memory

myName 31415962

↝

memory locations

We have also seen how to print things on a dialog window using alert.

Homework

Below you have the JavaScript code we have worked with today. Make sure to copy&paste it in your HTML live editor inside the content of the <script> tag. Do the homework stated at the end of this code sample. When you are done, print the code in a PDF file and send it to me as an attachment. Note: Make sure the PDF file shows all the code in your page!

print("Hello World!") ;

// Variable : consists in a "name" and a "value"

var x = 3 ; //Store '3' somewhere in the memory of the computer and label that memory location with the label 'x'.

//'var' is called a 'keyword'

print(x);

var myName = "John" ; //Store the string of characters 'John' somewhere in the memory of the computer and give that memory location the label 'nyName'

print(myName) ;

//alert

alert("Hello "+myName) ; //Opens a pop-up dialog window where it prints the word 'Hello ' followed by the content of the variable labeled 'myName'

alert("I am "+15+" years old.") ; //We can concatenate several strings and numbers together.

/*
This is a comment that extends over
several
lines.
But it does not affect the execution of the program.
*/

/*Exercise:
1) define a variable labeled 'mySchool' and assign it the value 'Dragon School'
2) Then open an alert dialog saying 'This is Computer Science at' and make it concatenate the content of 'mySchool'

Solution:
*/
var mySchool = "Dragon School" ;

alert('This is Computer Science at ' + mySchool) ;

/*Homework

1) Without deleting anything on this page, modify it so that only the last alert dialog shows up.

2) Define a new variable with label 'year' and value 2017.

3) Modify the last 'alert' dialog so that it appends at the end the value of 'year' -but make sure there is a space between this value and that of 'mySchool'. 
*/

Introduction to JavaScript

Review

Today

Code:

Computer Memory

Homework