陳述式與宣告

For an alphabetical listing see the sidebar on the left.

Block

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

break

中斷當下的迴圈、條件判斷（switch）或是標籤（label）陳述式，並將程式流程轉到被中斷陳述式後的陳述式。

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 (en-US)

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

if...else

當特定的條件為真時執行一段陳述式，若為假則另一段陳述式就會被執行。

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.

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.

function (en-US)

用指定的變數宣告一個函數

function*

Generators functions enable writing iterators (en-US) more easily.

async function

Declares an async function with the specified parameters.

return

Specifies the value to be returned by a function.

class (en-US)

Declares a class.

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.

已棄用 非標準 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 (en-US)

Iterates over iterable objects (including arrays, array-like objects, iterators and generators (en-US)), 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.

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.

已棄用 with (en-US)

Extends the scope chain for a statement.

• 運算式與運算子