Standard JavaScript objects.

Event

The event object represents the state of the event that is associated with the object at a given time. This object contains a set of properties that hold additional information about the event that occurred. Although all event properties are available to all event objects, some properties don't have any meaning for various events. In other words, not all of the properties are relevant to each type of event.

We'll consider several properties of the event object. You can find the complete list for IE in other documentation.

• srcElement This property contains the reference to the object that initiated the event. It can be used if several different elements can generate the same event and we need to figure out which one actually did.
• type This property contains information about type of the event. It can be useful if one event handler serves several different events. In this case we can identify what kind of event actually occurred. For example:

  if( event.type == "click" ){
   do this
  }	  	  

• clientX and clientY properties specify the X and Y coordinates of the mouse cursor at the time of the event, with respect to the target's object page (the browser window). These properties are very useful if you want to make an element move together with the mouse cursor. For example, we can define onMouseMove handler and change posLeft posTop coordinates of the object according to these clientX and clientY values. For example:

  function mouse_move_handler()
  {
    document.all['move_obj_id'].style. posTop = event.clientY;
    document.all['move_obj_id'].style. posLeft = event.clientX;
  }	  

  There is a complete example here.
• keyCode contains a number associated with the key that caused the event. This property is intended to be used with KeyDown, KeyUp, and KeyPress events. By using this property we can control what the user types in our form text input elements:

  Code	Result
  function key_pressed() { document.inform.showcode.value += "Code: "+event.keyCode+ " char: "+String.fromCharCode(event.keyCode)+"\n"; } ... <form name=inform> <INPUT name=num TYPE=TEXT SIZE=25 onKeyPress="key_pressed();"> <br><br> <textarea name=showcode rows=5 cols=40 onKeyPress="return false;"></textarea> </form>

  Since this property is writable, that is, the handler can assign another value instead of the one user pressed we can full control over user's input. This example shows how to use it to filter the input.
• altKey, ctrlKey, and shiftKey properties contain boolean values specifying whether the corresponding key is pressed. You can modify the previous example to print this additional information.
• cancelBubble property contains a boolean value that specifies whether the current event should bubble up the hierarchy of event handlers. See the event tutor for getting an idea about bubbling up. If you do not want to pass the event to the upper level handler set this property to true:

  event.cancelBubble = true;

  This property can be very useful if both a parent element and a child element have event handlers for the same event, but you do not want the parent to handle the events occurred on the child element.
• returnValue contains a boolean value that specifies whether the event should be handled by the default handle as well. For example, if we want to control user's input in an text input element we can define onKeyPress handler like we did before, but since this element has its own default handler, then the same key will be treated by that event handler. If we don't want this to happen we can set the returnValue property to false. For example, let's create an input element which allows the user types only digits in it:

  Code	Result
  <form> <input type=text onKeyPress="if( event.keyCode<48 || event.keyCode>57 ) event.returnValue=false;"> </form>

These are several links to documents discussing JavaScript events and event object:

var str = "my string";
var i = str.length;   // now i equals 9
var j = "wow".length; // now j equals 3 

var str = String.fromCharCode(109, 121, 32, 115, 116, 114, 105, 110, 103);

string_object_name.method_name()

String.method_name()

<form>
 <input type=text id=uinp size=5> 
 <input type=button value=" + 4 = " 
        onClick="document.all['res'].value = document.all['uinp'].value+4;">
 <input type=text id=res size=5>

var count = parseInt("123");
var hex_num = parseInt("AF3A", 16);

var avg = parseFloat("123.34");

var str = "af34.34";
var x = parseFloat(str);
if( isNaN(x) )
  alert("Error: '"+str+"' is not a floating point number");
else
  alert(x+" is a valid number");

var x = 15;
var str = x.toString();
var str2 = x.toString(2);

str= x.toString(16);