Javascript Introduction
JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Firefox, Chrome, Opera, and Safari.
Java and JavaScript are two completely different languages in both concept and design!
Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.
JavaScript was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all browsers since 1996.
The official standardization was adopted by the ECMA organization (an industry standardization association) in 1997.
The ECMA standard (called ECMAScript-262) was approved as an international ISO (ISO/IEC 16262) standard in 1998.
The development is still in progress.
Javascript How to
<html>
<body>
<h1>My First Web Page</h1>
<script type="text/javascript">
document.write("<p>" + Date() + "</p>");
</script>
</body>
</html>
Note: To manipulate HTML elements JavaScript uses the DOM method getElementById(). This method access the element with the specified id.
Inside the <script> tag use the type attribute to define the scripting language.
The <script> and </script> tells where the JavaScript starts and ends:
<html>
<body>
<h1>My First Web Page</h1>
<p id="demo">This is a paragraph.</p>
<script type="text/javascript">
... some JavaScript code ...
</script></body>
</html>
The lines between the <script> and </script> contains the JavaScript and are executed by the browser.
In this case the browser will replace the content of the HTML element with id="demo", with the current date:
<html>
<body>
<h1>My First Web Page</h1>
<p id="demo">This is a paragraph.</p>
<script type="text/javascript">
document.getElementById("demo").innerHTML=Date();
</script></body>
</html>
Without the <script> tag(s), the browser will treat "document.getElementById("demo").innerHTML=Date();" as pure text and just write it to the page:
To prevent them from doing this, and as a part of the JavaScript standard, the HTML comment tag should be used to "hide" the JavaScript.
Just add an HTML comment tag <!-- before the first JavaScript statement, and a --> (end of comment) after the last JavaScript statement, like this:
<html>
<body>
<script type="text/javascript">
<!--
document.getElementById("demo").innerHTML=Date();
//-->
</script></body>
</html>
The two forward slashes at the end of comment line (//) is the JavaScript comment symbol. This prevents JavaScript from executing the --> tag.
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JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Firefox, Chrome, Opera, and Safari.
What is JavaScript?
- JavaScript was designed to add interactivity to HTML pages
- JavaScript is a scripting language
- A scripting language is a lightweight programming language
- JavaScript is usually embedded directly into HTML pages
- JavaScript is an interpreted language (means that scripts execute without preliminary compilation)
- Everyone can use JavaScript without purchasing a license
Are Java and JavaScript the same?
NO!Java and JavaScript are two completely different languages in both concept and design!
Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.
What can a JavaScript do?
- JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages
- JavaScript can put dynamic text into an HTML page - A JavaScript statement like this: document.write("<h1>" + name + "</h1>") can write a variable text into an HTML page
- JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
- JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element
- JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing
- JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
- JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer
JavaScript = ECMAScript
JavaScript is an implementation of the ECMAScript language standard. ECMA-262 is the official JavaScript standard.JavaScript was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all browsers since 1996.
The official standardization was adopted by the ECMA organization (an industry standardization association) in 1997.
The ECMA standard (called ECMAScript-262) was approved as an international ISO (ISO/IEC 16262) standard in 1998.
The development is still in progress.
Javascript How to
The HTML <script> tag is used to insert a JavaScript into an HTML page.
Writing to The HTML Document
The example below writes a <p> element with current date information to the HTML document:<html>
<body>
<h1>My First Web Page</h1>
<script type="text/javascript">
document.write("<p>" + Date() + "</p>");
</script>
</body>
</html>
Note: To manipulate HTML elements JavaScript uses the DOM method getElementById(). This method access the element with the specified id.
Examples Explained
To insert a JavaScript into an HTML page, use the <script> tag.Inside the <script> tag use the type attribute to define the scripting language.
The <script> and </script> tells where the JavaScript starts and ends:
<html>
<body>
<h1>My First Web Page</h1>
<p id="demo">This is a paragraph.</p>
<script type="text/javascript">
... some JavaScript code ...
</script></body>
</html>
The lines between the <script> and </script> contains the JavaScript and are executed by the browser.
In this case the browser will replace the content of the HTML element with id="demo", with the current date:
<html>
<body>
<h1>My First Web Page</h1>
<p id="demo">This is a paragraph.</p>
<script type="text/javascript">
document.getElementById("demo").innerHTML=Date();
</script></body>
</html>
Without the <script> tag(s), the browser will treat "document.getElementById("demo").innerHTML=Date();" as pure text and just write it to the page:
Some Browsers do Not Support JavaScript
Browsers that do not support JavaScript, will display JavaScript as page content.To prevent them from doing this, and as a part of the JavaScript standard, the HTML comment tag should be used to "hide" the JavaScript.
Just add an HTML comment tag <!-- before the first JavaScript statement, and a --> (end of comment) after the last JavaScript statement, like this:
<html>
<body>
<script type="text/javascript">
<!--
document.getElementById("demo").innerHTML=Date();
//-->
</script></body>
</html>
The two forward slashes at the end of comment line (//) is the JavaScript comment symbol. This prevents JavaScript from executing the --> tag.
Next Class -->>
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