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JavaScript Statements and Declarations

JavaScript applications consist of statements with an appropriate syntax.

JavaScript statements are "instructions" to be "executed" by the web browser.

A single statement may span multiple lines.

Multiple statements may occur on a single line if each statement is separated by a semicolon.

This statement tells the browser to write "Hello world" inside an HTML element with id="para":

Run code

You can learn more about statements in our JavaScript Statements Tutorial.

Below is a list of JavaScript statements and declarations by category:

Declarations

Statement Description
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

Control flow

Statement Description
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
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

Iterations

Statement Description
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
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...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