I have a page with several checkboxes. I check a few of them and go to the next page, when I come back on this page, these checkboxes need to remain checked as they were before navigating to another page. Need to do it with Javascript. Any clue??
A:
You'll need to persist them between page-requests. You can use sessions or cookies to do this. What type of server are you working on, and with what type of server-side language?
Previous questions on SO have address writing/reading cookies from javacript.
Jonathan Sampson
2009-07-20 15:30:19
+1
A:
If you're limited to JavaScript only and no server side language I think you are left to read/writing cookies to maintain the state. As others have referenced, server side technologies are much better at this but if you must:
JavaScript cookie sample code (reference: http://www.quirksmode.org/js/cookies.html) :
function createCookie(name,value,days) {
if (days) {
var date = new Date();
date.setTime(date.getTime()+(days*24*60*60*1000));
var expires = "; expires="+date.toGMTString();
}
else var expires = "";
document.cookie = name+"="+value+expires+"; path=/";
}
function readCookie(name) {
var nameEQ = name + "=";
var ca = document.cookie.split(';');
for(var i=0;i < ca.length;i++) {
var c = ca[i];
while (c.charAt(0)==' ') c = c.substring(1,c.length);
if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
}
return null;
}
function eraseCookie(name) {
createCookie(name,"",-1);
}
brendan
2009-07-20 15:37:18
A:
I don't think there's any reasonably complicated way to do it without having any access to the server-side code, because at the minimum you need to install your code and also identify the HTML controls e.g. in order to check them. I 'm giving reasonable code that does what you want below.
Important notes:
- The code requires that each checkbox is given a distinct id attribute.
- The check state is stored in a cookie named 'JS_PERSISTENCE_COOKIE'. It would be better to store the name of this cookie in a variable instead of hardcoding it in a couple of separate places as I have done. What kind of variable should store the name depends on your app and requirements.
- It would be better to package the code inside an object instead of as a bunch of free functions as I have done. However, this is not relevant to your initial question.
- After clicking some checkboxes, you can simulate "navigating back to this page" by hitting CTRL+F5. F5 alone is not enough.
Here's the code and some sample HTML for testing:
<body onload="restorePersistedCheckBoxes()">
<input type="checkbox" id="check1" onclick="persistCheckBox(this)" />
<input type="checkbox" id="check2" onclick="persistCheckBox(this)" />
<input type="checkbox" id="check3" onclick="persistCheckBox(this)" />
<input type="button" value="Check cookie"
onclick="alert(document.cookie)" />
<input type="button" value="Clear cookie"
onclick="clearPersistenceCookie()" />
<script type="text/javascript">
// This function reads the cookie and checks/unchecks all elements
// that have been stored inside. It will NOT mess with checkboxes
// whose state has not yet been recorded at all.
function restorePersistedCheckBoxes() {
var aStatus = getPersistedCheckStatus();
for(var i = 0; i < aStatus.length; i++) {
var aPair = aStatus[i].split(':');
var el = document.getElementById(aPair[0]);
if(el) {
el.checked = aPair[1] == '1';
}
}
}
// This function takes as input an input type="checkbox" element and
// stores its check state in the persistence cookie. It is smart
// enough to add or replace the state as appropriate, and not affect
// the stored state of other checkboxes.
function persistCheckBox(el) {
var found = false;
var currentStateFragment = el.id + ':' + (el.checked ? '1' : '0');
var aStatus = getPersistedCheckStatus();
for(var i = 0; i < aStatus.length; i++) {
var aPair = aStatus[i].split(':');
if(aPair[0] == el.id) {
// State for this checkbox was already present; replace it
aStatus[i] = currentStateFragment;
found = true;
break;
}
}
if(!found) {
// State for this checkbox wasn't present; add it
aStatus.push(currentStateFragment);
}
// Now that the array has our info stored, persist it
setPersistedCheckStatus(aStatus);
}
// This function simply returns the checkbox persistence status as
// an array of strings. "Hides" the fact that the data is stored
// in a cookie.
function getPersistedCheckStatus() {
var stored = getPersistenceCookie();
return stored.split(',');
}
// This function stores an array of strings that represents the
// checkbox persistence status. "Hides" the fact that the data is stored
// in a cookie.
function setPersistedCheckStatus(aStatus) {
setPersistenceCookie(aStatus.join(','));
}
// Retrieve the value of the persistence cookie.
function getPersistenceCookie()
{
// cookies are separated by semicolons
var aCookie = document.cookie.split('; ');
for (var i=0; i < aCookie.length; i++)
{
// a name/value pair (a crumb) is separated by an equal sign
var aCrumb = aCookie[i].split('=');
if ('JS_PERSISTENCE_COOKIE' == aCrumb[0])
return unescape(aCrumb[1]);
}
return ''; // cookie does not exist
}
// Sets the value of the persistence cookie.
// Does not affect other cookies that may be present.
function setPersistenceCookie(sValue) {
document.cookie = 'JS_PERSISTENCE_COOKIE=' + escape(sValue);
}
// Removes the persistence cookie.
function clearPersistenceCookie() {
document.cookie = 'JS_PERSISTENCE_COOKIE=' +
';expires=Fri, 31 Dec 1999 23:59:59 GMT;';
}
</script>
</body>
Jon
2009-07-20 16:26:05
A:
Thanks folks for the answers,but i am not suppose to use ciikies as well,so better i prefer it to be done in ASP.net.
If you can't use cookies nor server side programming this is simply not possible. HTTP is a stateless protocol and requires the aid of server side sessions or cookies to add the state you require.
Josh
2009-07-22 02:27:39