this在客户端环境下什么含义
<form name="everything"> <!-- A one-of-everything HTML form... --><table border="border" cellpadding="5"> <!-- in a big HTML table -->
<tr>
<td>Username:<br>[1]<input type="text" name="username" size="15"></td>
<td>Password:<br>[2]<input type="password" name="password" size="15"></td>
<td rowspan="4">Input Events[3]<br>
<textarea name="textarea" rows="20" cols="28"></textarea></td>
<td rowspan="4" align="center" valign="center">
[9]<input type="button" value="Clear" name="clearbutton"><br>
[10]<input type="submit" name="submitbutton" value="Submit"><br>
[11]<input type="reset" name="resetbutton" value="Reset"></td></tr>
<tr>
<td colspan="2">
Filename: [4]<input type="file" name="file" size="15"></td></tr>
<tr>
<td>My Computer Peripherals:<br>
[5]<input type="checkbox" name="peripherals" value="modem">56K Modem<br>
[5]<input type="checkbox" name="peripherals" value="printer">Printer<br>
[5]<input type="checkbox" name="peripherals" value="tape">Tape Backup</td>
<td>My Web Browser:<br>
[6]<input type="radio" name="browser" value="nn">Netscape<br>
[6]<input type="radio" name="browser" value="ie">Internet Explorer<br>
[6]<input type="radio" name="browser" value="other">Other</td></tr>
<tr>
<td>My Hobbies:[7]<br>
<select multiple="multiple" name="hobbies" size="4">
<option value="programming">Hacking JavaScript
<option value="surfing">Surfing the Web
<option value="caffeine">Drinking Coffee
<option value="annoying">Annoying my Friends
</select></td>
<td align="center" valign="center">My Favorite Color:<br>[8]
<select name="color">
<option value="red">Red <option value="green">Green
<option value="blue">Blue <option value="white">White
<option value="violet">Violet <option value="peach">Peach
</select></td></tr>
</table>
</form>
<div align="center"> <!-- Another table--the key to the one above -->
<table border="4" bgcolor="pink" cellspacing="1" cellpadding="4">
<tr>
<td align="center"><b>Form Elements</b></td>
<td>[1] Text</td> <td>[2] Password</td> <td>[3] Textarea</td>
<td>[4] FileUpload</td> <td>[5] Checkbox</td></tr>
<tr>
<td>[6] Radio</td> <td>[7] Select (list)</td>
<td>[8] Select (menu)</td> <td>[9] Button</td>
<td>[10] Submit</td> <td>[11] Reset</td></tr>
</table>
</div>
<script>
// This generic function appends details of an event to the big Textarea
// element in the form above. It is called from various event handlers.
function report(element, event) {
var elmtname = element.name;
if ((element.type == "select-one") || (element.type == "select-multiple")){
value = " ";
for(var i = 0; i < element.options.length; i++)
if (element.options[i].selected)
value += element.options[i].value + " ";
}
else if (element.type == "textarea") value = "...";
else value = element.value;
var msg = event + ": " + elmtname + ' (' + value + ')\n';
var t = element.form.textarea;
t.value = t.value + msg;
}
// This function adds a bunch of event handlers to every element in a form.
// It doesn't bother checking to see if the element supports the event handler,
// it just adds them all. Note that the event handlers call report( ) above.
// Note that we're defining event handlers by assigning functions to the
// properties of JavaScript objects rather than by assigning strings to
// the attributes of HTML elements.
function addhandlers(f) {
// Loop through all the elements in the form
for(var i = 0; i < f.elements.length; i++) {
var e = f.elements[i];
e.onclick = function( ) { report(this, 'Click'); }
e.onchange = function( ) { report(this, 'Change'); }
e.onfocus = function( ) { report(this, 'Focus'); }
e.onblur = function( ) { report(this, 'Blur'); }
e.onselect = function( ) { report(this, 'Select'); }
}
// Define some special-case event handlers for the three buttons:
f.clearbutton.onclick = function( ) {
this.form.textarea.value=''; report(this,'Click');
}
f.submitbutton.onclick = function ( ) {
report(this, 'Click'); return false;
}
f.resetbutton.onclick = function( ) {
this.form.reset( ); report(this, 'Click'); return false;
}
}
// Finally, activate our form by adding all possible event handlers!
addhandlers(document.everything);
</script>
中e.onclick ，e.onfocus等等事件处理器代码中this的含义什么。。很困惑。给小弟讲讲，先谢谢了。。。
