Variables

General

Info:

• Variables are containers for storing values.

• A JavaScript variable can hold any type of data.

• usage

  1. Always declare variables at the beginning of a script

  2. Always use const if the value should not be changed

  3. Always use const if the type should not be changed (Arrays and Objects)

  4. Only use let if you can't use const

  5. Only use var if you MUST support old browsers.

• Any variable can be emptied, by setting the value to undefined. The type will also be undefined.

  car = undefined;    // Value is undefined, type is undefined

Identifiers

Info:

• use camel case for identifiers
• use descriptive names like totalSum
• Names can begin with a letter, $ or _

Danger:

• Identifiers are used to name variables and keywords, and functions.
• JavaScript is Case Sensitive
  • lastName and lastname are two different identifiers
• Names must begin with a letter.
  • _ commonly used for private / hidden variables
• Reserved words cannot be used as names.

let

Info:

• let has Block Scope
• Redeclaring in another block IS allowed

Danger:

• must be Declared before use
• cannot be redeclared in same block

var

Info:

• var has global Scope, it is hoisted and can be used everywhere
• can be redeclared

Danger:

• (re)declaration inside a { } block
• can be accessed from outside the block
• changes value globally

const

Info:

• const has Block Scope
• Redeclaring in another block IS allowed

Danger:

• must be Declared before use
• cannot be redeclared in same block