[monderJS] let, const, and var

Learned

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1. Variables
2. let,var,and const

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Variables

• A variable is a "names storage" for data. We can use variables to store goodies, visitors, and other data
• We can declare multiple variables in many different ways but have to consider eradability.

let user = 'MJ',
let age = '99',
let message = 'wanna go home';

Let

• When the value is changed, the old data is removed from the variable

let message;

message = 'I study better at night';

// old data is removed and the value changed
message = 'I'll study in the morning when I'm fresh'

alert(message);

• We can also declare two variables and copy data from one into the other

let hello = 'Hello MJ';

let message;

message = hello; // copy 'Hello MJ' from hello into message

// Now two variables hold the same data
alert(hello) // Hello MJ
alert(message) // Hello MJ

Var

• In order scripts, you may also find another keyword "var" instead of let

var message = 'Hello'; 

• The var keyword is almost the same as let.
  - It also declares a variable, but in a slightly different way
  • we'll get back to this topic later

Constants

• To declare a constant (unchanging) variable, use const instead of let:
• There is a widespread practice to use constants as aliases for difficult-to-remember values that are known prior to execution
• Such constants are named using capital letters and underscores

const COLOR_RED = "#FOO";

Summary

• We can declare variables to store data by using the var, let, or const keywords.
• var variables can be updated and re-declated within its scope
• let variables can be updated but not re-declared.
• const variables can neither be updated nor re-declared.

Tasks

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• Working with variables

1. Declare two variables: admin and name.
2. Assign the value "John" to name.
3. Copy the value from name to admin
4. Show the value of admin using alert (must output "John")

// How I did
let admin;
let name = "John";
admin = name;

alert(admin)

// Soln
let admin, name; // ahh I could've declared two variables at once!!
name = "John";
admin = name;

alert(admin)

• Uppercase const
  - Would it be right to use upper case for birthday? for age? Or even both?

const birthday = '18.04.1982';

const age = someCode(birthday);

• The value of birthday is hard-coded whereas variable "age" is evaluated in run-time. Therefore, it would be proper to use uppercase to birthday only.