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Questa sezione riguardante JavaScript contiene informazioni riguardo a tale linguaggio. Leggi altre informazioni riguardo a questa documentazione.
Oggetti globali
Questo capitolo documenta tutti gli oggetti standard predefiniti di JavaScript, con i loro metodi e le loro proprietà.
Valori
Varabili globali che rappresentano un valore semplice, non hanno altre proprietà o metodi.
Funzioni
Queste funzioni globali che vengono richiamate direttamente restituiscono direttamente il risultato al chiamante
eval()
uneval()
isFinite()
isNaN()
parseFloat()
parseInt()
decodeURI()
decodeURIComponent()
encodeURI()
encodeURIComponent()
escape()
unescape()
Oggetti fondamentali
Oggetti generali di Javascrpt, sui quali sono basati tutti gli altri oggetti. Rappresentano oggetti, funzioni ed errori.
Object
Function
Boolean
Symbol
Error
EvalError
InternalError
RangeError
ReferenceError
SyntaxError
TypeError
URIError
Numeri e date
Oggetti usati per rappresentare numeri, date e calcoli matematici.
Elaborazione del testo
Oggetti che rappresentano le stringe o il supporto per manipolarle.
Collezioni ordinate
Questi oggetti rappresentano delle collezioni di dati che sono ordinati secondo un indice. Includono array tipizzati ed costruttori simili ad array.
Array
Int8Array
Uint8Array
Uint8ClampedArray
Int16Array
Uint16Array
Int32Array
Uint32Array
Float32Array
Float64Array
Collezioni chiave-valore
Oggetti che rappresentano collezzioni che usano delle chiavi per identificarne gli elementi; si può iterare attraverso gli elementi nell'ordine in cui sono stati inseriti.
Dati strutturati
Oggetti che rappresentano e interagiscono con buffer di dati e con dati codificati utilizzando JavaScript Object Notation (JSON).
Oggetti di controllo dell'astrazione
Reflection
Internazionalizzazione
Oggetti aggiunti a ECMAScript per le funzionalità che dipendono dalla lingua.
WebAssembly
WebAssembly
WebAssembly.Module
WebAssembly.Instance
WebAssembly.Memory
WebAssembly.Table
WebAssembly.CompileError
WebAssembly.LinkError
WebAssembly.RuntimeError
Altro
Statements
Questo capitolo documenta tutti gli statements e le dichiarazioni JavaScript.
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
orcontinue
statement.
-
with
- Extends the scope chain for a statement.
Espressioni e operatori
Questo capitolo documenta espresisioni e operatori di JavaScript.
Expressions and operators by category
For an alphabetical listing see the sidebar on the left.
Primary expressions
Basic keywords and general expressions in JavaScript.
this
- The
this
keyword refers to the function's execution context. function
- The
function
keyword defines a function expression. -
class
- The
class
keyword defines a class expression. -
function*
- The
function*
keyword defines a generator function expression. -
yield
- Pause and resume a generator function
-
yield*
- Delegate to another generator function or iterable object.
[]
- 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
andobject["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.
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.
Binary logical operators
Logical operators are typically used with boolean (logical) values, and when they are, they return a boolean value.
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 oneyield
expression. - Expression closures
- The expression closure syntax is a shorthand for writing simple function.
Funzioni
Questo capitolo documenta come usare le funzioni in JavaScript.