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© 2015 PayPal Inc. All rights reserved. Confidential and proprietary.
JavaScript Fundamentals
Deepank Vora
June/03/2015 SST

© 2015 PayPal Inc. All rights reserved. Confidential and proprietary.
Introduction

The language
• Frontend -> Backend
• World’s most misunderstood language

Lab 0: Our first JavaScript program!
Write a program that prints out “Hello” to the console. Since this is the first lab, we
provide the answer for you! Just copy the below code:
console.log("Hello");

Comments
• Write something meant to be read by humans only (not the computer)
• Everything after // is a comment
console.log("Hello"); // This statement is a comment

Data Types

Data Types
• Number
• String
• Boolean
• Object
• Function
• Array

Number
• Number can be with, or without decimals
• Example
console.log(1);
console.log(2.5);

String
• Simply a series of characters
• Written with quotes (single or double)
Examples
console.log("Hello");
"JavaScript Rocks".length; // 16
"JavaScript Rocks".charAt(0); // "J"
"JavaScript Rocks".replace("JavaScript", "Java"); // "Java Rocks"
"JavaScript Rocks".toLowerCase(); // "javascript rocks"

Boolean
• true or false
• Example
console.log(true); // true
console.log(false); // false

Variables
var greeting = "Hello";
console.log(greeting);
greeting = "Hello, how are you?"
console.log(greeting);

Arithmetic operators
• Add
console.log(10 + 2)
• Subtract
console.log(10 - 2)
• Multiply
console.log(10 * 2)
• Divide
console.log(10 / 2)

= and == are completely different!
•= (assignment) : stores the value on RHS to the
variable on LHS
greeting = "Hello, how are you?"
•== (comparison) : compares LHS and RHS and
returns boolean (true or false)
console.log(1 == 1)

Array
var a = ["cat", "dog", "mouse"];
console.log(a[0]); // ?
console.log(a[2]); // ?

null and undefined
• null: Deliberate non-value
var x = null;
console.log(x); // null
• undefined: uninitialized value
var x;
console.log(x); // undefined

Quiz
What is the output of the program?
var list = [5, 10];
var x = list[0] + list[1];
var y = list[1] - list[0];
var z = y / x;
console.log(z);

Control Structures
If-else
if (time < 10) {
greeting = "Good morning";
} else if (time < 20){
greeting = "Good day";
} else {
greeting = "Good evening";
}

Objects
• Simply a collection of name-value pairs
var dog = { breed:"labrador", color:"brown"};
dog.name = "Tommy";
console.log(dog.name); // ?
console.log(dog.breed); // ?

Lab 1
Create an object person with properties, firstName “Harry”, lastName “Potter”.
Print the firstName of person.

Function
function max(x, y){
if(x>y){
return x;
}
else{
return y;
}
}
var a = max(2, 4);
console.log(a);

Lab 2
Write a function min that returns the minimum of two numbers.
Call the function with two numbers. Use console.log to print the result and check if
it is correct.

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Editor's Notes