Values

A VALUE is a location in computer memory that stores DATA.

There are many kinds of values, including String, Number, Array, Object, and more.

The different kinds of values are called TYPES

Numbers

A number is what it sounds like -- any integer or decimal.

10
-12
3.14

Lab: Playing with Numbers

Open up a node environment in your terminal (node Enter). Once you're in the node environment you should be able to write javascript, and run it inside your terminal. Try out the following equations:

• Add two numbers together with the + operator
• Multiply two numbers with the * operator
• Divide two numbers using the / operator
• Square a number by raising it to the power of 2 **2
• Create a more complex mathematical equation. Useing amixture of different operators
• Bonus: Weird math! Try the following equations:
  • 0.1 + 0.2, 2**53 and 2**53 + 1, and Infinity - Infinity

What have you noticed about math in JavaScript

Strings

A string is an object that's a collection of characters, like a word or a sentence.

'apple'
'banana'
'Cherry Pie'

String Slicing

You can extract sub-parts of a string using slice

// "slice from character 0 to character 4"
"blueberry".slice(0, 4) 

// "slice from character 4 to the end
"blueberry".slice(4)

The first number is which character to start from.

The second number is which character to end on.

MDN: slice

String Indexing

Indexes are the positions of characters within a String.

| B | L | U | E | B | E | R | R | Y |
0   1   2   3   4   5   6   7   8   9

Then 'blueberry'.slice(0, 4)

• Includes the characters to the right of the start index
• Includes the characters to the left of the end index
• And excludes the character to the right of the end index

Experiment with different start and end values in the console.

Lab: Playing with Strings

Either open a terminal, and run node, or create a new JavaScript file in a text editor.

Complete the following challenges

• Add two strings together with the same type of quotes

e.g. 'Java' + 'Script'

• Add two strings together with different types of quotes

e.g. "I'm double quoted!" + 'I am single quoted.'

• Subtract two strings

e.g. 'cats' - 'dogs'

• Add a string to a number

• Try to put more quotes inside your a string's quotes?

Booleans

A Boolean is a value that is either TRUE or FALSE, and are represented with the values true and false

Created by George Boole, a mathematician who invented Boolean algebra.)

Booleans and Conditionals

A conditional starts with the keyword if followed by a test in parentheses if (10 > 5), followed by a block of code defined by curly braces which runs if the check evaluates to true.

Lab: Is it True?

Given the conditional answer the following questions.

if (someValueHere) {
  console.log('It is truthy');
}

• Is the boolean true truthy?
  • how about false?
• Try replacing true with a string
  • Is it truthy?
• Try replacing true with a number
  • Is it true?
  • What about the number 0?
• Try replacing true with the expression 1 < 2
  • What happens if you switch the operator like so 1 > 2?

Operators

Values can be combined or manipulated using operators

• PLUS (+)
• TIMES (*)
• POWER (**)
• DOT (.)
• ASSIGNMENT (=)
• COMPARISON (===)

An operator sends a message to the value

• e.g. 1 + 2 sends the number 1 the message please add 2 to yourself.

The DOT operator ., is a special operator that can send any message

Comments

Two slashes in a row means everything after these slashes is a comment.

2 + 2 // returns 4

JavaScript ignores everything to the right of the comment

Allowing for an explanation of what the nearby code does, or why it does it.

(2 + 2) * 3 // first add, then muliply

/* 
This is a
multi-line
comment
*/
console.log(x /*some variable from earlier*/);

Expression Evaluation

Code that results in a value is called an EXPRESSION

When JavaScript encounters an expression, it evaluates it. Evaluates means, to convert to a value.

Complex expressions with values and operators apply the operators until it results in a single value.

2 + 2 * 3 // Question: What is 2 + 2 * 3?
          // Answer: 8

// Question: What is the uppercase version of 'apple'?
'apple'.toUpperCase()  
// Answer: "APPLE"

Return Values

Evaluating an expression RETURNS a value

This value can be assigned to a variable, or used in another way.

let product = 4 * 4; // product is 16