JavaScript: Variables and Functions

JS
Variables
and
Func1ons

Jussi
Pohjolainen

Tampere
University
of
Applied
Sciences

Datatypes

•  Numbers

•  Boolean

•  String

•  Null,
undeﬁned

•  Object

•  Func1on

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)

Hois1ng

•  Variables
are
moved
on
top
of
the
func1on!

function test() {
var x;
if(true) {
x = 5;
}
document.write(x);
}

Hois1ng

function test() {

document.write(x); // Prints undefined!

if(true) {
var x = 5;
}
}

Hois1ng

function test() {
var x;
document.write(x); // Prints undefined!

if(true) {
x = 5;
}
}

So
what
happens
here?

var x = 10;

function test() {
document.write(x);
if(true) {
var x = 5;
}
}

So
what
happens
here?

var x = 10;

function test() {
var x; // Overrides the global one..
document.write(x); // undefined
if(true) {
x = 5;
}
}

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;

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

Basic
Func1on

function add(a, b)
{
return a+b;
}
alert(add(1,2));

Func1on
as
Variable

var add = function(a, b)
{
return a+b;
}
alert(add(1,2));

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

JavaScript: Variables and Functions

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