JavaScript Statements

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

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JavaScript Statements

This statement tells the browser to write "Hello Dolly." inside an HTML element with id="demo":

Example

document.getElementById("demo").innerHTML = "Hello Dolly.";

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JavaScript Programs

Most JavaScript programs contain many JavaScript statements.

The statements are executed, one by one, in the same order as they are written.

In this example, x, y, and z is given values, and finally z is displayed:

Example

var x = 5;
var y = 6;
var z = x + y;
document.getElementById("demo").innerHTML = z;

	JavaScript programs (and JavaScript statements) are often called JavaScript code.

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Semicolons ;

Semicolons separate JavaScript statements.

Add a semicolon at the end of each executable statement:

a = 5;
b = 6;
c = a + b;

When separated by semicolons, multiple statements on one line are allowed:

a = 5; b = 6; c = a + b;

	On the web, you might see examples without semicolons. Ending statements with semicolon is not required, but highly recommended.

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JavaScript White Space

JavaScript ignores multiple spaces. You can add white space to your script to make it more readable.

The following lines are equivalent:

var person = "Hege";
var person="Hege";

A good practice is to put spaces around operators ( = + - * / ):

var x = y + z;

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JavaScript Line Length and Line Breaks

For best readability, programmers often like to avoid code lines longer than 80 characters.

If a JavaScript statement does not fit on one line, the best place to break it, is after an operator:

Example

document.getElementById("demo").innerHTML =
"Hello Dolly.";

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JavaScript Code Blocks

JavaScript statements can be grouped together in code blocks, inside curly brackets {...}.

The purpose of code blocks is to define statements to be executed together.

One place you will find statements grouped together in blocks, are in JavaScript functions:

Example

function myFunction() {
    document.getElementById("demo").innerHTML = "Hello Dolly.";
    document.getElementById("myDIV").innerHTML = "How are you?";
}

	In this tutorial we use 4 spaces of indentation for code blocks. You will learn more about functions later in this tutorial.

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JavaScript Keywords

JavaScript statements often start with a keyword to identify the JavaScript action to be performed.

Here is a list of some of the keywords you will learn about in this tutorial:

Keyword	Description
break	Terminates a switch or a loop
continue	Jumps out of a loop and starts at the top
debugger	Stops the execution of JavaScript, and calls (if available) the debugging function
do ... while	Executes a block of statements, and repeats the block, while a condition is true
for	Marks a block of statements to be executed, as long as a condition is true
function	Declares a function
if ... else	Marks a block of statements to be executed, depending on a condition
return	Exits a function
switch	Marks a block of statements to be executed, depending on different cases
try ... catch	Implements error handling to a block of statements
var	Declares a variable

	JavaScript keywords are reserved words. Reserved words cannot be used as names for variables.