Variáveis

Tipos de dados

JavaScript's type hierarchy

JavaScript for impatient programmers (Book)

Category	Types	Values
Primitive	Undefined	`undefined`
Primitive	Null	`null`
Primitive	Boolean	`true`, `false`
Primitive	Number	`-15` `15`, `0b1111`, `0o17`, `0xf` `-123.45` `123.45`, `1.2345e2`, `12345E-2`
Primitive	String	`'Hello'`, `"Hello"`, `Hello`
Object	Array	`[]` `[1, 2, 3]` `[1, '2', true, [3, false]]` `["Alice", "alice@email"]`
Object	Object	`{name: "Alice", email: "alice@email"}`

Declaração de variáveis

Linguagem C:

int number = 10;

int number = 10;

Linguagem Python:

number = 10

number = 10

Keyword

var number = 10;
console.log(number); //=> 10

var number = 10;
console.log(number); //=> 10

let number = 10;
console.log(number); //=> 10

let number = 10;
console.log(number); //=> 10

const number = 10;
console.log(number); //=> 10

const number = 10;
console.log(number); //=> 10

Reassociação

var number;
number = 10;
number = 100;
console.log(number); //=> 100

var number;
number = 10;
number = 100;
console.log(number); //=> 100

let number;
number = 10;
number = 100;
console.log(number); //=> 100

let number;
number = 10;
number = 100;
console.log(number); //=> 100

const number; // SyntaxError
const number = 10;
number = 100; // TypeError

const number; // SyntaxError
const number = 10;
number = 100; // TypeError

const numbers = [];
numbers.push(1);
console.log(numbers); //=> [ 1 ]

const numbers = [];
numbers.push(1);
console.log(numbers); //=> [ 1 ]

Escopo

var number = 10;
var number = 10;

var number = 10;
var number = 10;

let number = 10;
let number = 10; // SyntaxError: Identifier 'number' has already been declared

let number = 10;
let number = 10; // SyntaxError: Identifier 'number' has already been declared

const number = 10;
const number = 10; // SyntaxError: Identifier 'number' has already been declared

const number = 10;
const number = 10; // SyntaxError: Identifier 'number' has already been declared

Tipagem Dinâmica

let variable = 10;
console.log(variable); //=> 10
console.log(typeof variable); //=> number
 
variable = 'fulano';
console.log(variable); //=> 'fulano'
console.log(typeof variable); //=> string

let variable = 10;
console.log(variable); //=> 10
console.log(typeof variable); //=> number
 
variable = 'fulano';
console.log(variable); //=> 'fulano'
console.log(typeof variable); //=> string

Tipagem Fraca

const x = 10;
const y = '5';
console.log(x - y); //=> 5

const x = 10;
const y = '5';
console.log(x - y); //=> 5

Case Sensitive

const number = 8;
const Number = 80;
const NUMBER = 800;

const number = 8;
const Number = 80;
const NUMBER = 800;

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