Js fundamentals part 1 Modern Javascript

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JS FUNDAMENTALS PART 1
Modern Javascript

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In Javascript there are legal and illegal ways of naming a variable:
Legal way:
Must begin with a letter, underscore (_), or dollar sign ($).

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Can contain letters, numbers, underscores, or dollar signs.
Are case sensitive, meaning that "myVar" and "myvar" are two different
variables.
Should not use reserved keywords, such as "var", "function", "if", "else",
"while", "for", etc.
Illegal variable names:
Cannot begin with a number.
Cannot contain spaces or special characters (except underscore or dollar
sign).
Cannot use reserved keywords.
Cannot start with Capital letters.

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CamelCase is reccomended to use in Js => myFullname, isMarried...
const PI = 3.14; This variable works only in this case.
Naming variables must be descriptive:
const myFirstName = "Mirjalol"; 
cosnt myFirstJob = "Teacher"
Data Types
Variables that hold a value can be data type, not variable.

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Comments in Js

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This is multiline way of commenting 
Single line way of commenting 
let, var and const

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let can be reassigned, mutated. 
let book = "Alvido Vatan"; 
book = "Halol Luqma"; 
✅
let cannot be redaclared
let myFirstJob = "Teacher"; 
let myFirstJob = "Programmer";
❌
You can create Undefined variable with let. 
let code;
✅
Reccomanded one is const
variables that doesnt change are declared with const, u cannot reassign and
redaclare