JAVASCRIPT OUTPUT AND SYNTAX
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JAVASCRIPT OUTPUT AND SYNTAX
JavaScript does not have any built-in print or display functions.
Using document.write() after an HTML document is fully loaded, will delete all existing HTML:
The id attribute defines the HTML element. TheinnerHTML property defines the HTML content:
Activate the browser console with F12, and select "Console" in the menu.
SYNTAX
JavaScript syntax is the rules, how JavaScript programs are constructed.
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In a programming language, these program instructions are called statements.
JavaScript is a programming language.
JavaScript statements are separated by semicolon.
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try it
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Values, Operators, Expressions, Keywords, and Comments.
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Fixed values are called literals. Variable values are called variables.
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Numbers are written with or without decimals:
10.50
1001
Strings are text, written within double or single quotes:
"John Doe"
'John Doe'
Expressions can also represent fixed values:
5 + 6
5 * 10
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JavaScript uses the var keyword to define variables.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:
var x;
x = 6;
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var x = 5;
var y = 6;
JavaScript uses arithmetic operators ( + - * / ) tocompute values:
(5 + 6) * 10
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The var keyword tells the browser to create a new variable:
var x = 5 + 6;
var y = x * 10;
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Code after double slashes // or between /* and */ is treated as a comment.
Comments are ignored, and will not be executed:
var x = 5; // I will be executed
// var x = 6; I will NOT be executed
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The variables lastName and lastname, are two different variables.
lastName = "Doe";
lastname = "Peterson";
JavaScript does not interpret VAR or Var as the keyword var.
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Unicode covers (almost) all the characters, punctuations, and symbols in the world.
For a closer look, please study our [url=../charsets/ref_html_utf8.html]Complete Unicode Reference[/url].[/size]
JavaScript Display Possibilities
JavaScript can "display" data in different ways:- Writing into an alert box, using window.alert().
- Writing into the HTML output usingdocument.write().
- Writing into an HTML element, using innerHTML.
- Writing into the browser console, usingconsole.log().
Using window.alert()
You can use an alert box to display data:.Example
- Code:
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<script>
window.alert(5 + 6);
</script>
</body>
</html>
Using document.write()
For testing purposes, it is convenient to usedocument.write():Example
- Code:
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<script>
document.write(5 + 6);
</script>
</body>
</html>
Using document.write() after an HTML document is fully loaded, will delete all existing HTML:
Example
- Code:
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<button onclick="document.write(5 + 6)">Try it</button>
</body>
</html>
The document.write() method should be used only for testing. |
Using innerHTML
To access an HTML element, JavaScript can use thedocument.getElementById(id) method.The id attribute defines the HTML element. TheinnerHTML property defines the HTML content:
Example
- Code:
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My First Paragraph</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = 5 + 6;
</script>
</body>
</html>
In our examples, we often use the innerHTML method (writing into an HTML element). |
Using console.log()
In your browser, you can use the console.log() method to display data.Activate the browser console with F12, and select "Console" in the menu.
Example
- Code:
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<script>
console.log(5 + 6);
</script>
</body>
</html>
SYNTAX
JavaScript syntax is the rules, how JavaScript programs are constructed.
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JavaScript Programs
A computer program is a list of "instructions" to be "executed" by the computer.In a programming language, these program instructions are called statements.
JavaScript is a programming language.
JavaScript statements are separated by semicolon.
Example
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- Code:
<html>
<head>
<title>
my javascript
</title>
</head>
<body>
<script type="text/javascript" />
var x = 5;
var y = 6;
var z = x + y;
document.write(z);
</script>
</body>
</html>
try it
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In HTML, JavaScript programs can be executed by the web browser. |
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JavaScript Statements
JavaScript statements are composed of:Values, Operators, Expressions, Keywords, and Comments.
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JavaScript Values
The JavaScript syntax defines two types of values: Fixed values and variable values.Fixed values are called literals. Variable values are called variables.
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JavaScript Literals
The most important rules for writing fixed values are:Numbers are written with or without decimals:
10.50
1001
Strings are text, written within double or single quotes:
"John Doe"
'John Doe'
Expressions can also represent fixed values:
5 + 6
5 * 10
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JavaScript Variables
In a programming language, variables are used to storedata values.JavaScript uses the var keyword to define variables.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:
var x;
x = 6;
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JavaScript Operators
JavaScript uses an assignment operator ( = ) to assignvalues to variables:var x = 5;
var y = 6;
JavaScript uses arithmetic operators ( + - * / ) tocompute values:
(5 + 6) * 10
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JavaScript Keywords
JavaScript keywords are used to identify actions to be performed.The var keyword tells the browser to create a new variable:
var x = 5 + 6;
var y = x * 10;
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JavaScript Comments
Not all JavaScript statements are "executed".Code after double slashes // or between /* and */ is treated as a comment.
Comments are ignored, and will not be executed:
var x = 5; // I will be executed
// var x = 6; I will NOT be executed
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JavaScript is Case Sensitive
All JavaScript identifiers are case sensitive.The variables lastName and lastname, are two different variables.
lastName = "Doe";
lastname = "Peterson";
JavaScript does not interpret VAR or Var as the keyword var.
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It is common, in JavaScript, to use camelCase names. You will often see names written like lastName (instead of lastname). |
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JavaScript Character Set
JavaScript uses the Unicode character set.Unicode covers (almost) all the characters, punctuations, and symbols in the world.
For a closer look, please study our [url=../charsets/ref_html_utf8.html]Complete Unicode Reference[/url].[/size]
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