1. JS
Variables
and
Func1ons
Jussi
Pohjolainen
Tampere
University
of
Applied
Sciences

2. Datatypes
• Numbers
• Boolean
• String
• Null,
undefined
• Object
• Func1on

3. Variable
scope
• Global
and
local
variables
• JS
does
not
have
block
statement
scope!
function test() {
if(true) {
var x = 5;
}
document.write(x);
}
• This
works!
X
is
defined
in
the
scope
of
the
func1on
(or
globally)

4. Hois1ng
• Variables
are
moved
on
top
of
the
func1on!
function test() {
var x;
if(true) {
x = 5;
}
document.write(x);
}

5. Hois1ng
function test() {
document.write(x); // Prints undefined!
if(true) {
var x = 5;
}
}

6. Hois1ng
function test() {
var x;
document.write(x); // Prints undefined!
if(true) {
x = 5;
}
}

7. So
what
happens
here?
var x = 10;
function test() {
document.write(x);
if(true) {
var x = 5;
}
}

8. So
what
happens
here?
var x = 10;
function test() {
var x; // Overrides the global one..
document.write(x); // undefined
if(true) {
x = 5;
}
}

9. Global
Objects
• Global
variables
are
in
fact
proper1es
of
the
global
object!
•
In
web
pages
the
global
object
is
window
• So
– var
x
=
5
ó
window.x
=
5;

10. Objects
var Sales = "Toyota";
function CarTypes(name) {
if (name == "Honda")
return name;
else
return "Sorry, we don't sell " + name + ".";
}
var car = { myCar: "Saturn", getCar: CarTypes("Honda"), special: Sales };
document.write(car.myCar); // Saturn
document.write(car.getCar); // Honda
document.write(car.special); // Toyota

11. Basic
Func1on
function add(a, b)
{
return a+b;
}
alert(add(1,2));

12. Func1on
as
Variable
var add = function(a, b)
{
return a+b;
}
alert(add(1,2));

13. Func1on
as
Variable
var add=function theAdd(a, b)
{
return a+b;
}
alert(add(1,2)); // produces 3
alert(theAdd(1,2)); // also produces 3