Referência JavaScript

Onde encontrar mais informações sobre JavaScript ?

Você pode verificar a documentação do core da linguagem e seus novos recursos ( ECMAScript puro em sua maior parte), incluindo também :

• Guia de JavaScript
• Referência de JavaScript

Se você é novo com JavaScript, recomendamos à você começar com o guia. Uma vez que você já tenha uma base sobre os fundamentos da linguagem, você pode usar a referência para obter mais detalhes sobre objetos individuais e construtores da linguagem.

Estrutura da referência

Na referência do JavaScript você poderá encontrar os seguintes seções :

Padrões de objetos internos (built-in objects)

Esta seção documenta todos o padrão JavaScript de objetos internos, juntamente com seus métodos e propriedades.

Instruções e Declarações (Statements)

As aplicações em JavaScript consistem em declarações com uma sintaxe apropriada. Uma única declaração pode abranger várias linhas de código. Várias instruções podem ocorrer em uma única linha também, se cada declaração for devidamente separada por ponto e virgula. Instrução não é uma palavra-chave, mas sim, um grupo de palavras-chave.

Expressões e operadores

Esta seção documenta todos os operadores da linguagem JavaScript, expressões e palavras-chave.

Funções

Esta seção é referente as funções existentes no JavaScript.

Novo no JavaScript

Esta seção é sobre as versões do JavaScript, contendo o histórico de versões e o que há de novo nas proximas versões.

Mais paginas de referências

• Recursos e funcionalidades obsoletas
• Gramática Léxica
• Tipos e estruturas de dados

JavaScript applications consist of statements with an appropriate syntax. A single statement may span multiple lines. Multiple statements may occur on a single line if each statement is separated by a semicolon. This isn't a keyword, but a group of keywords.

Statements and declarations by category

For an alphabetical listing see the sidebar on the left.

Control flow

Block

A block statement is used to group zero or more statements. The block is delimited by a pair of curly brackets.

break

Terminates the current loop, switch, or label statement and transfers program control to the statement following the terminated statement.

continue

Terminates execution of the statements in the current iteration of the current or labeled loop, and continues execution of the loop with the next iteration.

Empty

An empty statement is used to provide no statement, although the JavaScript syntax would expect one.

if...else

Executes a statement if a specified condition is true. If the condition is false, another statement can be executed.

switch

Evaluates an expression, matching the expression's value to a case clause, and executes statements associated with that case.

throw

Throws a user-defined exception.

try...catch

Marks a block of statements to try, and specifies a response, should an exception be thrown.

Declarations

var

Declares a variable, optionally initializing it to a value.

let

Declares a block scope local variable, optionally initializing it to a value.

const

Declares a read-only named constant.

Functions and classes

function

Declares a function with the specified parameters.

function*

Generators functions enable writing iterators more easily.

return

Specifies the value to be returned by a function.

class

Declares a class.

Iterations

do...while

Creates a loop that executes a specified statement until the test condition evaluates to false. The condition is evaluated after executing the statement, resulting in the specified statement executing at least once.

for

Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.

for each...in

Iterates a specified variable over all values of object's properties. For each distinct property, a specified statement is executed.

for...in

Iterates over the enumerable properties of an object, in arbitrary order. For each distinct property, statements can be executed.

for...of

Iterates over iterable objects (including arrays, array-like objects, iterators and generators), invoking a custom iteration hook with statements to be executed for the value of each distinct property.

while

Creates a loop that executes a specified statement as long as the test condition evaluates to true. The condition is evaluated before executing the statement.

Others

debugger

Invokes any available debugging functionality. If no debugging functionality is available, this statement has no effect.

export

Used to export functions to make them available for imports in external modules, another scripts.

import

Used to import functions exported from an external module, another script.

label

Provides a statement with an identifier that you can refer to using a break or continue statement.

with

Extends the scope chain for a statement.

Specifications

See also

• Operators

Este capítulo documenta todos os operadores, expressões e keywords da linguagem JavaScript .

Expressões e operadores por categoria

Para uma lista alfabética ver a barra lateral à esquerda.

Expressões primárias

Palavras-chave e expressões básicas em JavaScript.

this

A palavra-chave this refere-se ao contexto de execução da função.

function

A palavra-chave function define uma função.

class

A palavra-chave class define uma classe.

function*

A palavra-chave function*  define um gerador de função.

yield

Pausa e retorma uma função de gerador

yield*

Delegar a outra função gerador ou objeto iterável.

[]

Array initializer/literal syntax.

{}

Object initializer/literal syntax.

/ab+c/i

Regular expression literal syntax.

[for (x of y) x]

Array comprehensions.

(for (x of y) y)

Generator comprehensions.

( )

Grouping operator.

Left-hand-side expressions

Left values are the destination of an assignment.

Property accessors

Member operators provide access to a property or method of an object
(object.property and object["property"]).

new

The new operator creates an instance of a constructor.

super

The super keyword calls the parent constructor.

...obj

The spread operator allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.

Increment and decrement

Postfix/prefix increment and postfix/prefix decrement operators.

A++

Postfix increment operator.

A--

Postfix decrement operator.

++A

Prefix increment operator.

--A

Prefix decrement operator.

Unary operators

A unary operation is operation with only one operand.

delete

The delete operator deletes a property from an object.

void

The void operator discards an expression's return value.

typeof

The typeof operator determines the type of a given object.

+

The unary plus operator converts its operand to Number type.

-

The unary negation operator converts its operand to Number type and then negates it.

~

Bitwise NOT operator.

!

Logical NOT operator.

Arithmetic operators

Arithmetic operators take numerical values (either literals or variables) as their operands and return a single numerical value.

+

Addition operator.

-

Subtraction operator.

/

Division operator.

*

Multiplication operator.

%

Remainder operator.

Relational operators

A comparison operator compares its operands and returns a Boolean value based on whether the comparison is true.

in

The in operator determines whether an object has a given property.

instanceof

The instanceof operator determines whether an object is an instance of another object.

<

Less than operator.

>

Greater than operator.

<=

Less than or equal operator.

>=

Greater than or equal operator.

Equality operators

The result of evaluating an equality operator is always of type Boolean based on whether the comparison is true.

==

Equality operator.

!=

Inequality operator.

===

Identity operator.

!==

Nonidentity operator.

Bitwise shift operators

Operations to shift all bits of the operand.

<<

Bitwise left shift operator.

>>

Bitwise right shift operator.

>>>

Bitwise unsigned right shift operator.

Binary bitwise operators

Bitwise operators treat their operands as a set of 32 bits (zeros and ones) and return standard JavaScript numerical values.

&

Bitwise AND.

|

Bitwise OR.

^

Bitwise XOR.

Operadores Lógicos Binários

Operadores lógicos são normalmente usados com boolean (logical) valores, e quando eles são, eles retornam um valor Boolean.

&&

AND.

||

 OR.

Conditional (ternary) operator

(condition ? ifTrue : ifFalse)

The conditional operator returns one of two values based on the logical value of the condition.

Assignment operators

An assignment operator assigns a value to its left operand based on the value of its right operand.

=

Assignment operator.

*=

Multiplication assignment.

/=

Division assignment.

%=

Remainder assignment.

+=

Addition assignment.

-=

Subtraction assignment

<<=

Left shift assignment.

>>=

Right shift assignment.

>>>=

Unsigned right shift assignment.

&=

Bitwise AND assignment.

^=

Bitwise XOR assignment.

|=

Bitwise OR assignment.

[a, b] = [1, 2]
{a, b} = {a:1, b:2}

Destructuring assignment allows you to assign the properties of an array or object to variables using syntax that looks similar to array or object literals.

Comma operator

,

The comma operator allows multiple expressions to be evaluated in a single statement and returns the result of the last expression.

Non-standard features

Legacy generator function

The function keyword can be used to define a legacy generator function inside an expression. To make the function a legacy generator, the function body should contains at least one yield expression.

Expression closures

The expression closure syntax is a shorthand for writing simple function.

Specifications

See also

• Operator precedence