JavaScript From Scratch
“Getting Your Feet Wet”

Agenda
• Variables
• Conditionals
• Loops
• Functions

Variables are...
• Storage Containers for Data
• Someone’s name
• A username/password
• The current time
• ... or anything else your application needs

var password = ‘mike is awesome’;

var name = ‘Mike G’;
var age = 25;
var isCool = true;

Conditionals are...
• A way to execute code conditionally
• If something is true, do this
• Otherwise, do that

var age = 25;
if (age < 21) {
alert(‘Go home’);
}

var age = 25;
if (age < 21) {
alert(‘Go home’);
}
else {
alert(‘Two drink minimum’);
}

Loops
• Loops allow code to run repeatedly
• Over and over and over...
• But only upon a condition

var start = 10;
var stop = 20;
var counter = start;
while (counter <= stop) {
alert(counter);
counter = counter + 1;
}

About those operators
=
var foo = 100;

About those operators
==
(foo == 100)

About those operators
<
(age < 21)

About those operators
>
(calories > 2000)

About those operators
<=
(age <= 21)

About those operators
>=
(calories >= 2000)

About those operators
&&
(age >= 25 && age <= 50)

About those operators
||
(name == ‘mike’ || name == ‘joe’)

Functions
• Store “blocks” of code so they can be
reused later
• Are one of the most powerful features of
the JavaScript language

function add () {
alert(2 + 2);
}
add();

function add (num1, num2) {
alert(num1 + num2);
}
add(2, 2);
add(42, 10);
add(123, 0);

function add (num1, num2) {
return num1 + num2;
}
var sum1 = add(2, 2);
var sum2 = add(42, 10);
var sum3 = add(123, 0);

Review
• Variables...
• Store data
• Begin with a var
• Are given names
• Are assigned values with =

Review
• Conditionals...
• Fork code execution based on a
condition
• Begin with an if
• Condition enclosed in (parenthesis)
• Blocks are enclosed in {curly braces}

Review
• Conditionals...
• Can use else to catch a failed
conditional

Review
• Loops...
• Repeatedly execute blocks of code
• Execute conditionally
• Come in many flavors:
• while, for, for in, do while

Review
• Functions...
• Store code for later use
• Can accept input parameters
(arguments).
• Can send output (return values).

Homework
• Build a micro-library which performs basic
math operations
• Functions should accept arguments and
return the result of the math operation

Homework
• Required Functions:
• add (num1, num2)
• subtract (num1, num2)
• multiply (num1, num2)
• divide (num1, num2)

Homework
• Required Functions:
• square (num)
• increment (num)
• decrement (num)
• power (num, power)