data operations

The most basic computation is an operation. These happen between 2 pieces of data and then you get another piece of data out.

Javascript defines certain specific types of data and the kinds of operations you can do on it.

Types of data:

  • numbers
  • booleans
  • strings
operations on numbers

Numbers are: 1,2,3,45.6, -6.7 etc.

+ - * /

2 + 2

Like normal math, Javascript follows the traditional order of operations: P.E.M.D.A.S. or "Please Excuse My Dear Aunt Sally." Mathematical operations are executed in the following order...

  1. Parenthetical expressions
  2. Exponentiation
  3. Multiplication
  4. Division
  5. Addition
  6. Subtraction
(4 + 2) * (12 / 3)
// => 6 * 4
// => 24

(8 / 4 * 2) + 1
// => (2 * 2) + 1
// => 5
operations on booleans

A boolean is true or false

var userCreated = true;

A boolean operation produces a new boolean value.

true === true // results in a new boolean value: true
operations on strings
+

"hello" + "world"

You can't, however, use other math operators on strings...

"hamburger" - "ham"
// => NaN

"hamburger" * 3
// => NaN

NaN ("Not a number")

A special number...that's not a number?

typeof NaN
// => Number

You usually get NaN when the result of a math operation is not real (e.g., dividing 0 by 0, multiplying strings together).

0/0
// => NaN

Non-Values

null is a value that indicates the lack of a meaningful value. There are no operations you can do to a null value.

Variables

We can assign values to variables using the assignment operator =.

var phrase = 'In my room is a chair and a table';

we can use that variable as a stand-in for the original value:

console.log(phrase);

phrase can be anything we want (with some syntactical caveats), sentence for example, whatever makes semantic sense.

var phrase = 'In my room is a chair and a table';
var sum = 99 + 1;

console.log(phrase);
console.log(phrase);
console.log(phrase);
console.log(phrase);

console.log(sum);
console.log(sum);
console.log(sum);
console.log(sum);

x4 => "In my room is a chair and a table"

x4 => 100

Variable names
  • cannot begin with a number or include special character
  • camelCase
    • thisVariable NOT this_variable
  • case sensitive
    • thisVariable is not the same as ThisVariable
Semicolons
  • The interpreter needs the semicolons. DO NOT FORGET THEM!
Variable re-assignment
var item = 'chair';

item = 'eclair';

console.log(item);

=> "eclair"

Variables as Data

The purpose of a variable is:

to represent it's literal value in a name that defines what it means.
contain dynamic data that changes but always represents the same thing. ex. var temperatureToday = 34;

Naming a variable for what it represents is a very hard problem.

One of your main tasks as a programmer is to come up with the most accurate, succinct name possible.

Operations on variables

var number = 3;
var square = number * number;
var cube = square *  number;

var distance = 100;
var startTime = 0;
var endTime = 100;
var totalTime = endTime = startTime;
var speed = distance / totalTime;

var pi = 3.14;
var radius = 3;
var area = pi * radius * radius;

Read error messages

Error messages are good. They are not adversarial! They are there to help you.

Error messages are clues that you learn to read. You should be able to read these clues on your own.

Create a new html file: touch error.html

Create a new js file: touch error.js

Link them together in your HTML file: <script src="error.js"></script>

Put this example in:

console.log('hello world);

The error that is created is typical. It looks intimidating and weird, but if you pry, you will find valuable clues. For example:

Error messages will tell you a specific line number where in the code the error occurred. This tells me the error is on line 1: script.js:1

Errors will often tell you what type of error. SyntaxError: Unexpected token ILLEGAL

You have to learn to sort the 'wheat from the chaff' so to speak. This will come with practice.

Errors are a growth opportunity. When you receive an error, yes it is an obstacle, but with a little patience it will turn you into a more informed, better developer.

pairing exercises

Open the chrome console.

Try the examples above. Combine the operators and see what values you get.

further

% (Modulus)

The modulus operator - % - returns the remainder of a division operation.

12 % 5
// => 2, which is the remainder of 12 / 5

Modulus has a pretty handy use case: to check if a number is even. We can do this by running NUMBER % 2. If a number is even, the result should be 0 (i.e., there should be no remainder).

4 % 2
// => 0, because 4 is even

5 % 2
// => , because 5 is odd. When 5 is divided by 2, the remainder is 1.

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