Data Types, Variables and Arrays

Objectives

• understand the history of JavaScript and its purpose as a language
• conceptualize JavaScript variables and data structures
• utilize primitives and operators in order to solve problems using JavaScript

History

Then

• developed by Brendan Eich (for Netscape, now Mozilla)
• 10 days
• went through a few different names before settling on JavaScript (Java was popular)
• taken to ECMA for standardization

Now

• JavaScript is THE front-end language
• clunky, things to complain about, but it works and is web-driven!
• tons of open source libraries
• also used as a backend language, using Node.js
• working on ECMAScript 6

Comments

Comments come in two forms

Line comments

// descriptive stuff

Multi-line comments

/**
  These
  are
  comments on
  many lines
*/

Numbers

Numbers are one of the types of values we want to be able to interact and play with in JS.

Integers

 ..., -1, 0, 2, 3, 4, 5, ...

Floats (or Decimal numbers)

 2.718, 3.14, .5, .25, etc

In JS these are both the same type of object, which it calls Numbers.

This can infrequently cause problems!

0.1 * 0.2 = 0.020000000000000004

How to deal with floating point precision in JavaScript

Exercise

2 + 2 * 3

How would you get the 2 + 2 to execute before the * 3? In other words, how would you change this expression to get 12?

Strings

Strings are collections of letters and symbols known as Characters, and we use them to deal with words and text in Javascript. Strings are just another type of value in Javascript.

"John"
'Jane'

Exercise

You can use operators on strings too! Try typing "John" + "Jane". This is called String concatenation

Tangent: Type coercion

Try this...

"1" + 1

Without removing the quotes, how would you get this to equal 2?

Booleans

Booleans are a type that can only have one of two values: true or false.

true
false

Operator Review

+ (add)
- (subtract)
* (multiply)
/ (divide)
% (modulus)

Special Number Operators

Javascript can be a little cheap with the number of operations it allows you to do. For example, how is someone supposed to square a number or cube a number easily? Luckily there is a special Math object with some very useful methods.

• Taking a number to some power? Then just use Math.pow

// 3^2 becomes
Math.pow(3,2);
// => 9

// 2^4 becomes
Math.pow(2,4);
// => 16

• Taking a square root

// √(4) becomes
Math.sqrt(4);
// => 2

• Need a random number? Then use Math.random.

// The following only returns a random decimal
Math.random();
// => .229375290430

/**
  The following will return a
  random number between 0 and 10
*/
Math.random() * 10;

• Since Numbers can be Floats or Integers we often want to get rid of remaining decimal places, which can be done using Math.floor.

// Remove the decimal
Math.floor(3.14)
// => 3

Math.floor(3.9999)
// => 3

Variables

Having made some expressions it becomes evident we want to store these values.

var myNumber = 1;
// or also

var myString = "Greetings y'all!";

The main note to make here is that these variables should always have the var keyword and use camelCase

Extra Readings

In-class example on variables: https://gist.github.com/anonymous/374b65facd27b296829cf7634fc9f65e

Reference

Values, variables, and literals

re-introduction to JavaScript

MDN JavaScript documentation