JavaScript

The following section of JavaScript will detect if anyone is viewing your page in a frame. If they are then the code will redirect them to your site. It essentially stops people using frames to poach your content and stops online proxy software from viewing your site.

if (top.location != location) {
 top.location.href = document.location.href;
}

All you have to do is include this code either in your script tag or your JavaScript includes. Quite a neat little trick really.

To get the class of an element with JavaScript you use the className property of the element object. Take the following section of HTML code.

<div id="adiv" class="theClass">some text</div>

Use the following bit of code to print off the class name of the div element in a message box.

alert(document.getElementById('adiv').className);

To set the class name to something else you can use the same property, but in this case just pass it a value. The following example changes the class name of the div element to 'newClass'.

A good usability feature of web forms is to fill the contents of one drop down menu, depending on what has been selected in a previous menu. This can be done quite easily with JavaScript.

Take the following form, in this instance I have used some server variables used in mod_rewrite, but the idea is valid.

If you have lots of check boxes in a row a handy little usability trick is to allow a user to click on a button and check all of the checkboxes at once. The following function will either check or uncheck all of the check boxes in your form.

function check_uncheck(truefalse){
 var boxes = document.forms[0].chkboxarray.length;
 var form = document.getElementById('checkForm');
 for(var i=0;i < boxes;i++){
  if (truefalse) {
   form.chkboxarray[i].checked=true;
  } else {
   form.chkboxarray[i].checked=false;
  }
 }
}

All you need to do is to add two buttons to your form that will allow users to either check or uncheck the boxes on the form. The function takes a single parameter, which is what to set the value of the check boxes to, so one button is needed to set them to checked and one to unchecked.

Creating a form as part of an AJAX control is a common practice, but when you include a submit button within the form the default behaviour of the form is to redirect to the destination supplied in action. To run a form using JavaScript you need to include two things.

<form action="javascript:return false;" method="post" id="analysisForm" >

In order to overwrite the normal operation of a form you will need to replace the action attribute with some JavaScript code that returns false. This is can be done in the form of come in-line JavaScript code (commonly called a bookmarklet) in the place of any URL in the action attribute of the form.

Next, in order to actually get JavaScript to intercept the form submission action an onsubmit event is added to the form tag.

When writing JavaScript applications I normally write for loops like this.

for (var i = 0; i < elements.length; ++i) {
  // loop...
}

There isn't anything wrong with this, but it is not an efficient way of doing things. All it takes is a little knowledge of what the for loop does every time it runs. The loop can be split into three sections like this.