Storing & Manipulating Data With Variables

Variables are containers for storing data.  A variable name is a label that points to this data that will allow you to access and manipulate this stored data. Creating a variable is called declaring it. You declare a variable in JavaScript by using the var keyword. Generally it’s best practice to declare all variables at the beginning of a script. All variables must be identified with a unique name. To assign a value to the variable, use the = sign. A variable declared without a value will have the value undefined. It’s best practice to end all lines of code in JavaScript with a ; semicolon.  It’s not required but it’s considered best practice.

There are 3 ways to declare a variable in JavaScript.

• Var: Global Scope – Can be accessed from anywhere.
• Let: Local Scope – Only lets you use the variable within the block you declared it in. (Best practice to avoid naming collisions)
• Const: A variable that can not be changed.

The general rules for creating names for variables are:

• Variable names can contain letters, digits, underscores, or a dollar sign.
• Names must begin with a letter and not a number.
• Names can also begin with $ (but that’s usually reserved for JQuery)
• Names are case sensitive so (Price and price are different variables)
• Reserved keywords cannot be used as variable names.
• It’s best practice to use Camel Case for variable names. First letter of the first word is small. First letter of all following words should be capitalized.

JavaScript Provides 7 Different Data Types:

You can get the type of a variable using the typeof keyword: typeof variable;

• undefined: variable that hasn’t been defined.
• null: Means nothing. Set a variable to be nothing.
• boolean: Set a variable to true or false.
• number: Variable that contains any number.
• string: Variable that contains any text.
• symbol: A symbol may be used as an identifier for object properties and dynamically produces an anonymous, unique value.
• object: An object can store key value pairs.

Escape characters inside a sting.

Some chatacters don't work inside a sting and need to be escaped to work.

Bracket Notion

Get a character within a specific index of the string. Remember that javaScript uses ZERO BASED INDEXING which starts at 0 not 1.

Numbers & Variables In Javascript

In JavaScript, just like in algebra, we can use variables in an expression.