陳述式與宣告
JavaScript 應用程式由適當的陳述式組成。一個單一的陳述式可以跨用好幾行。 多個陳述式也可以藉由分號分隔來寫在同一行。 這不是一個關鍵字,而是一群關鍵字。
陳述式與宣告分類
For an alphabetical listing see the sidebar on the left.
流程控制
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
(en-US)- 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
(en-US)- Marks a block of statements to try, and specifies a response, should an exception be thrown.
宣告
函數與類別(Class)
function
(en-US)- 用指定的變數宣告一個函數
function*
- Generators functions enable writing iterators 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.
迭代(Iteration)
do...while
(en-US)- 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
(en-US)- Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.
-
Deprecated
Non-Standard
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), invoking a custom iteration hook with statements to be executed for the value of each distinct property.
while
(en-US)- 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.
其他
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. -
Deprecated
with
(en-US) - Extends the scope chain for a statement.
瀏覽器相容性
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