JavaScript statements are composed of:
- Values,
- Operators,
- Expressions,
- Keywords and
- Comments.
The following statement tells the browser to write "Hello JavaScript." inside an HTML element with id="example":
Example:
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Statement Example</h2>
<p>In this Example, JavaScript statements are executed by the browser.</p>
<p id="demo"></p>
<script>
document.getElementById("example").innerHTML = "Hello JavaScript.";
</script>
</body>
</html>
Most JavaScript programs contain many JavaScript statements.
Note: JavaScript programs (and JavaScript statements) are often called JavaScript code.
Semicolons ( ; ):
Semicolons separate JavaScript statements. You should add a semicolon at the end of each executable statement.
Example:
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Semicolons</h2>
<p>JavaScript Semicolons separates JavaScript Statemant.</p>
<p id="example"></p>
<script>
var x, y, z;
x = 10;
y = 12;
z = x + y;
document.getElementById("example").innerHTML = z;
</script>
</body>
</html>
Multiple statements on one line are allowed, When separated by semicolons:
Example:
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Semicolons</h2>
<p>JavaScript Semicolons separates JavaScript Statemant.</p>
<p id="example"></p>
<script>
var x, y, z;
x = 11; y = 13; z = x + y;
document.getElementById("example").innerHTML = z;
</script>
</body>
</html>
JavaScript White Space:
JavaScript ignores multiple spaces. To make it more readable just add white space to your script. The following lines are equivalent:
var person = "amit";
var person="amit";
Put spaces around operators ( = + - * / ) is a good practice.
Example:
var a = b + c;
var person = "amit";
JavaScript Comments:
To make Code more readable and explain JavaScript code use javascript comments.
Two Types of Comments in JavaScript:
- Single Line Comments
- Multi-line Comments
Single Line Comments:
Single line comments start with //.
Javascript can not execute the comments line
Example of single line comment:
<!DOCTYPE html>
<html>
<body>
<h1 id="id1"></h1>
<p id="id2"></p>
<script>
// Change heading
document.getElementById("id1").innerHTML = "JavaScript Single Line Comments";
// Change paragraph
document.getElementById("id2").innerHTML = "A Simple paragraph.";
</script>
</body>
</html>
Example of single line comment:
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Single Line Comments</h2>
<p id="example"></p>
<script>
var a = 10; // Declare a, give it the value of 10
var b = a + 2; // Declare b, give it the value of a + 2
document.getElementById("example").innerHTML = b; // Write b to example
</script>
</body>
</html>
Multi-line Comments:
It start with /* and end with */.
Ignored by JavaScript if any text between /* and */ will be.
Example of Multi line comment:
<!DOCTYPE html>
<html>
<body>
<h1 id="heading1"></h1>
<p id="paragraph1"></p>
<script>
/* The code below will change
the heading with id = "heading1"
and the paragraph with id = "paragraph1" */
document.getElementById("heading1").innerHTML = "JavaScript Multi Line Comments";
document.getElementById("paragraph1").innerHTML = "A Simple paragraph."; </script>
</body>
</html>
Note: Multi Line Comments are often used for formal documentation.
Project Source Code:
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Statements, Semicolons, White Space and Comments</h2>
<p id="example"></p>
</body>
</html>
<script type="text/javascript">
var x, y, z; // that is a statement
x = 5; // that is also statement
y = 6; // that is also statement
z = x + y; // ; samicolon
// - single line comment
/*-multi line comment*/
// ; semicolon
alert(z);
alert(z);
</script>
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