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Javascript. CS 236369, Spring 2010. What is Javascript ?. Browser scripting language Dynamic page creation Interactive Embedded into HTML pages Javascript is NOT Java Different syntax Different programming concepts Javascript runs on client-side (browser) only.
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Javascript CS 236369, Spring 2010
What is Javascript ? • Browser scripting language • Dynamic page creation • Interactive • Embedded into HTML pages • Javascript is NOT Java • Different syntax • Different programming concepts • Javascript runs on client-side (browser) only
Adding Javascript to HTML • All Javascript code must be inside <script> • Old browsers do not support Javascript • Example: <html> <script language=“javascript”> <!-- document.write(“<h1>Hello World</h1>”); --> </script> <script language=“text/javascript” src=“myscript.js” /> </html>
Programming concept • No static types • Everything is an associative array • Every variable can hold attributes • No access limitations (i.e no private attributes) • Functions are variables • Dynamic binding • Inheritance is possible (though complicated and incomplete)
Variables example var x = 1; // define a numeral variable x = “123”; // x is now a string x = new Object(); // x is now an object x.attr = “val”; // x now has the attribute ‘attr’ x.f = function() { document.write(“a”); }; // x now has a function named ‘f’ x.f(); // f is invoked
Functions • Defined by the keyword ‘function’ • No return type and no argument types • Can be invoked with any number of arguments • Example: function f(x) { alert(x); } f(‘abc’); // result will be an alert box with ‘abc’ f(); // result will be an alert box with ‘undefined’ f(‘abc’, ‘edf’); // result will be an alert box with ‘abc’
Execution • Javascript code may be executed in 2 different cases: • Upon parsing the page, when the browser encounters javascript code not inside a function Example: <script type=“javascript”> document.write(‘<h1>Hi</h1>’); </script> • Events (next slide)
Events • Javascript can be activated on certain events • When a page is loaded • When a button is clicked • When a form is submitted • And many more … • Example: function f() { alert(‘clicked !’); } <input type=“button” onclick=“f();” value=“go!”/>
Events • Consider the following example <div id=“outer” onclick=“f();”> <div id=“inner” onclick=“g();”>click me</div> </div> • Which javascript function should be invoked first? • Netscape answer: f • Firefox answer: default g, can be changed to f • Microsoft Explorer: g
Events (form submission example) function validate_required(field, alerttxt) {if (field .value==null|| field.value==“”) { alert(alerttxt); return false;}return true; } function validate_form(form) { if (validate_required(form.email,”Email is requred”)==false) { return false; } return true; }
Events (form submission cont) <html> <head> <script type=“javascript” src=“example.js” /> </head> <body> <form action=“submit.jsp” onsubmit=“return validate_form(this);”> Email: <input type="text" name="email" size="30"> <input type="submit" value="Submit"> </form> </body> </html>
DOM • Javascript has built in access to the html document DOM tree • Every element in the html document can be removed or modified • New elements can be inserted to the html document dynamically
DOM Example <html><head> <script language="javascript"> function f() { var elmt = document.createElement('h1'); var txtNode = document.createTextNode('new element'); elmt.appendChild(txtNode); document.getElementById('someId').appendChild(elmt); } </script></head> <body> <input type="button" onclick="f();" value="click" /> <div id="someId" /></body></html>
References and tutorials • http://www.w3schools.com/jsref/dom_obj_document.asp • http://www.w3schools.com/js/default.asp • http://www.javascriptkit.com/javatutors/closures.shtml • http://www.webreference.com/js/column79/
