JavaScript Statements and Declarations

A JavaScript application is composed of statements with proper grammar.

JavaScript statements are "instructions" that web browsers need to "execute".

A statement can span multiple lines.

If each statement is separated by a semicolon, multiple statements may appear on one line.

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

Example

document.getElementById("para").innerHTML = "Hello world";

You can find in ourIn the JavaScript statements tutorialLearn more about statements.

The following is a list of JavaScript statements and declarations listed by category:

Variable declaration

Declaration	Description
var	Declare a variable, which can optionally be initialized with a value
let	Declare a block {} scoped local variable, which can optionally be initialized with a value
const	Declare a read-only named constant

Statement	Description
break	Terminate the current loop, switch, or label statement, and pass control to the statement after the terminating statement.
continue	Terminate the execution of a statement in the current loop or the current iteration of a labeled loop, and continue executing the loop in the next iteration.
if...else	If the specified condition is true, execute a statement. If the condition is false, another statement can be executed.
switch	Calculate the expression so that the value of the expression matches the case clause, and execute the statement related to the case
throw	Throw a user-defined exception
try...catch	Mark the statement block to be attempted and specify the response when an exception is thrown

Statement	Description
while	Create a loop that executes the specified statement as long as the computed result of the test condition is true. The condition is checked before the statement is executed
do...while	Create a loop that executes the specified statement until the value of the test condition is false. The statement is executed first, and then the condition is evaluated, so the specified statement is executed at least once
for	Create a loop consisting of three optional expressions, enclosed in parentheses and separated by semicolons, followed by the statement to be executed in the loop
for...in	Traverse the enumerable properties of an object in arbitrary order. For each different property, you can execute a statement
for...of	Iterate over iterable objects (including arrays, array-like objects, iterators, and generators), call custom iteration hooks, and execute statements for each different property value