Develop Reference

Check if multiple divs are visible at once

I have been using the following code to check if a div is visible:
if ($("#monday").is(':visible')) {
document.getElementById('scheduleitem1').style.width = 540;
$("#scheduleitem1").show();
}
That code worked fine. However I want to check if one of multiple divs are visible at once.
I've tried the following codes which did not work:
if ($("#monday" || "#tuesday").is(':visible')) {
document.getElementById('scheduleitem1').style.width = 540;
$("#scheduleitem1").show();
}
and
if ($("#monday", "#tuesday").is(':visible')) {
document.getElementById('scheduleitem1').style.width = 540;
$("#scheduleitem1").show();
}
So how do I do if I want to check if one of multiple divs are visible at once?

Try this :
$("#monday,#tuesday").is(':visible')
http://api.jquery.com/is/ : "... return true if at least one of these elements matches the given arguments".

Check length of selected elements $("#monday,#tuesday").find(":visible").length == 1
Something like
if ($("#monday,#tuesday").find(":visible").length == 1) {
document.getElementById('scheduleitem1').style.width = 540;
$("#scheduleitem1").show();
}

Try this:
if ($("#monday").is(':visible') || $("#tuesday").is(':visible')) {
$("#scheduleitem1").css('width', '540px').show();
}
I would add a wrapper to all week days and do something like this:
if($("#weekDays").find('div:visible')) {
$("#scheduleitem1").css('width', '540px').show();
}

I'm aware the question states that only one element must be visible.
This answer is for future visitors who want to check if all the elements are visible.
// Assume that the elements are visible
var is_visible = true;
// Select the elements wanted and go through each of them one by one
$("#monday, #tuesday, #etc").each(function() {
// Check that the assumption is true for each element selected
if (!$(this).is(':visible')) {
is_visible = false;
}
});
if (is_visible) {
$("#scheduleitem1").width(540).show();
}
Update, for brevity:
// Check if the elements are not hidden.
if (!$("#monday, #tuesday, #etc").is(':hidden')) {
$("#scheduleitem1").width(540).show();
}

jquery wrap, append, prepend to parent div

I am trying to detect when a certain div element has a height of 0 in order to display a div element with a message.
function checkads()
{
if ($('#container').height() == 0)
{
$('.wp_bannerize').wrap($('<div id="notice">ENABLE ADS</div>'));
};
}
$(document).ready(checkads);
The above works fine, however, is there anyway to make the script wrap the parent div that is 1 or 2 levels above the child div without having to define the class name of the parent manually "wp_bannerize"

You could try something like this:
function checkads() {
var $container = $('#container');
if ($container.height() == 0) {
$container.parent().wrap($('<div id="notice">ENABLE ADS</div>'));
// OR $container.parent().parent().wrap($('<div id="notice">ENABLE ADS</div>'));
}
}
Or change your checkads() function to:
function checkads($current) {
if ($current.height() == 0) {
$current.parent().wrap($('<div id="notice">ENABLE ADS</div>'));
}
}
And call it like:
checkads($('#container');
checkads($('#container2');
//etc...

You can use $('#container').parent().parent() to find the parent of the parent, for example. You can also use $('#container').closest('div') to search through the parent list for the closest div (or whatever). You don't need to know the class name (although you can also use that with closest!)

jQuery, selecting just number from id like "article-23"

All right, I have a div tag which got a class="blog-post" and id like id="article-23" (where "23" could be any number, as it is id of blog post in a database). I need to somehow get just a number from that id and than apply some rules to that div tag. So say:
if number from id % 2 == 0 {
set text colour black to associated div tag with class of blog-post
} else {
set text colour white to associated div tag with class of blog-post
}
Thats just a "pseudo" code to show logic that I wan't to apply dependent if number from id is even or odd, but the question remains same, how do I just get number from id like "article-23" ?

As simple as
var number = "article-23".match(/\d+/)[0];
But you have to be sure that any digit exists in the string, otherwise you'd get a error.

You can actually apply rules via function, which makes this the cleanest solution (in my opinion):
$(".blog-post").css('color', function () {
return +this.id.replace('article-', '') % 2 ? 'blue' : 'red';
});
http://jsfiddle.net/ExplosionPIlls/Jrc5u/

Try this:
$('.blog-post[id^="article-"]').each(function () {
if (parseInt(this.id.replace('article-', '')) % 2 === 0) {
$('#' + this.id).css('color', 'black');
} else {
$('#' + this.id).css('color', 'white');
}
});
jsFiddle Demo

As an alternative, HTML5 supports these things called "data attributes", which are specifically meant for attaching data to your DOM without abusing things like the "class" or "id" attributes. jQuery provides a handy .data method for reading these attributes in a more obvious way.
You can add your own numeric ID attribute using something like "data-id":
<div class="blog-post" data-id="23" />
$("#blog-post").each(function () {
console.log($(this).data("id")); // Look up the data-id attribute
});

If I'm understanding correctly, you want the number after the hyphen of the id tag of your .blog-post class.
var article = $(".blog-post").attr('id'); //get the id
var article = article.split("-"); // split it on hyphens
return article = article[article.length-1]; // return the last element

Can someone explain the following javascript code?

In addition to the explanation, what does the $ mean in javascript? Here is the code:
var ZebraTable = {
bgcolor: '',
classname: '',
stripe: function(el) {
if (!$(el)) return;
var rows = $(el).getElementsByTagName('tr');
for (var i=1,len=rows.length;i<len;i++) {
if (i % 2 == 0) rows[i].className = 'alt';
Event.add(rows[i],'mouseover',function() {
ZebraTable.mouseover(this); });
Event.add(rows[i],'mouseout',function() { ZebraTable.mouseout(this); });
}
},
mouseover: function(row) {
this.bgcolor = row.style.backgroundColor;
this.classname = row.className;
addClassName(row,'over');
},
mouseout: function(row) {
removeClassName(row,'over');
addClassName(row,this.classname);
row.style.backgroundColor = this.bgcolor;
}
}
window.onload = function() {
ZebraTable.stripe('mytable');
}
Here is a link to where I got the code and you can view a demo on the page. It does not appear to be using any framework. I was actually going through a JQuery tutorial that took this code and used JQuery on it to do the table striping. Here is the link:
http://v3.thewatchmakerproject.com/journal/309/stripe-your-tables-the-oo-way

Can someone explain the following
javascript code?
//Shorthand for document.getElementById
function $(id) {
return document.getElementById(id);
}
var ZebraTable = {
bgcolor: '',
classname: '',
stripe: function(el) {
//if the el cannot be found, return
if (!$(el)) return;
//get all the <tr> elements of the table
var rows = $(el).getElementsByTagName('tr');
//for each <tr> element
for (var i=1,len=rows.length;i<len;i++) {
//for every second row, set the className of the <tr> element to 'alt'
if (i % 2 == 0) rows[i].className = 'alt';
//add a mouseOver event to change the row className when rolling over the <tr> element
Event.add(rows[i],'mouseover',function() {
ZebraTable.mouseover(this);
});
//add a mouseOut event to revert the row className when rolling out of the <tr> element
Event.add(rows[i],'mouseout',function() {
ZebraTable.mouseout(this);
});
}
},
//the <tr> mouse over function
mouseover: function(row) {
//save the row's old background color in the ZebraTable.bgcolor variable
this.bgcolor = row.style.backgroundColor;
//save the row's className in the ZebraTable.classname variable
this.classname = row.className;
//add the 'over' class to the className property
//addClassName is some other function that handles this
addClassName(row,'over');
},
mouseout: function(row) {
//remove the 'over' class form the className of the row
removeClassName(row,'over');
//add the previous className that was stored in the ZebraTable.classname variable
addClassName(row,this.classname);
//set the background color back to the value that was stored in the ZebraTable.bgcolor variable
row.style.backgroundColor = this.bgcolor;
}
}
window.onload = function() {
//once the page is loaded, "stripe" the "mytable" element
ZebraTable.stripe('mytable');
}

The $ doesn't mean anything in Javascript, but it's a valid function name and several libraries use it as their all-encompassing function, for example Prototype and jQuery

From the example you linked to:
function $() {
var elements = new Array();
for (var i=0;i<arguments.length;i++) {
var element = arguments[i];
if (typeof element == 'string') element = document.getElementById(element);
if (arguments.length == 1) return element;
elements.push(element);
}
return elements;
}
The $ function is searching for elements by their id attribute.

This function loops through the rows in a table and does two things.
1) sets up alternating row style. if (i % 2 == 0) rows[i].className = 'alt' means every other row has its classname set to alt.
2) Attaches a mouseover and mouseout event to the row so the row changes background color when the user mouses over it.
the $ is a function set up by various javascript frameworks ( such as jquery) that simply calls document.getElementById

The code basically sets alternating table rows to have a different CSS class, and adds a mouseover and mouseout event change to a third css class, highlighting the row under the mouse.
I'm not sure if jQuery, prototype or maybe another third party JS library is referenced, but the dollar sign is used by jQuery as a selector. In this case, the user is testing to see if the object is null.

$ is the so-called "dollar function", used in a number of JavaScript frameworks to find an element and/or "wrap" it so that it can be used with framework functions and classes. I don't recognize the other functions used, so I can't tell you exactly which framework this is using, but my first guess would be Prototype or Dojo. (It certainly isn't jQuery.)

The code creates a ZebraTable "object" in Javascript, which stripes a table row by row in Javascript.
It has a couple of member functions of note:
stripe(el) - you pass in an element el, which is assumed to be a table. It gets all <tr> tags within the table (getElementsByTagName), then loops through them, assigning the class name "alt" to alternating rows. It also adds event handlers for mouse over and mouse out.
mouseover(row) - The "mouse over" event handler for a row, which stores the old class and background colour for the row, then assigns it the class name "over"
mouseout(row) - The reverse of mouseover, restores the old class name and background colour.
The $ is a function which returns an element given either the elements name or the element itself. It returns null if its parameters are invalid (non-existent element, for example)
I believe the framework being used is Prototype, so you can check out their docs for more info

Have a look at the bottom of the article that you have got the code from, you'll see that they say you'll also need prototype's $ function. From article
In your CSS you’ll need to specify a
default style for table rows, plus
tr.alt and tr.over classes. Here’s a
simple demo, which also includes the
other functions you’ll need (an Event
registration object and Prototype’s $
function).

IE javascript error - possibly related to setAttribute?

I am using Safalra's javascript to create a collapsible list. The script works across several browsers with no problem. However, when I apply the javascript to my own list, it fails to act as expected when I use IE (I'm using 7 at the moment). It simply writes the list, without the expand and contract images.
I copied the Safalra's javascript precisely, so I assume the error must be in my own list. This is how I generated my list:
<body onLoad="makeCollapsible(document.getElementById('libguides'));">
<ul id="libguides">
<script type="text/javascript" src="http://api.libguides.com/api_subjects.php?iid=54&more=false&format=js&guides=true&break=li"></script>
</ul>
(Yes, I do close the body tag eventually.) When I run this in IE, it tells me that line 48 is causing the problem, which appears to be:
node.onclick=createToggleFunction(node,list);
Here's the entire function:
function makeCollapsible(listElement){
// removed list item bullets and the sapce they occupy
listElement.style.listStyle='none';
listElement.style.marginLeft='0';
listElement.style.paddingLeft='0';
// loop over all child elements of the list
var child=listElement.firstChild;
while (child!=null){
// only process li elements (and not text elements)
if (child.nodeType==1){
// build a list of child ol and ul elements and hide them
var list=new Array();
var grandchild=child.firstChild;
while (grandchild!=null){
if (grandchild.tagName=='OL' || grandchild.tagName=='UL'){
grandchild.style.display='none';
list.push(grandchild);
}
grandchild=grandchild.nextSibling;
}
// add toggle buttons
var node=document.createElement('img');
node.setAttribute('src',CLOSED_IMAGE);
node.setAttribute('class','collapsibleClosed');
node.onclick=createToggleFunction(node,list);
child.insertBefore(node,child.firstChild);
}
I confess I'm too much of a javascript novice to understand why that particular line of code is causing the error. I looked at some of the other questions here, and was wondering if it might be a problem with setAttribute?
Thanks in advance.
Edited to add:
Here's the code for the createToggleFunction function. The whole of the script is just these two functions (plus declaring variables for the images).
function createToggleFunction(toggleElement,sublistElements){
return function(){
// toggle status of toggle gadget
if (toggleElement.getAttribute('class')=='collapsibleClosed'){
toggleElement.setAttribute('class','collapsibleOpen');
toggleElement.setAttribute('src',OPEN_IMAGE);
}else{
toggleElement.setAttribute('class','collapsibleClosed');
toggleElement.setAttribute('src',CLOSED_IMAGE);
}
// toggle display of sublists
for (var i=0;i<sublistElements.length;i++){
sublistElements[i].style.display=
(sublistElements[i].style.display=='block')?'none':'block';
}
}
}
Edited to add (again):
Per David's suggestion, I changed all instances of setAttribute & getAttribute...but clearly I did something wrong. IE is breaking at the 1st line (which is simply the doctype declaration) and at line 49, which is the same line of code where it was breaking before:
node.onclick=createToggleFunction(node,list);
Here's the first function as written now:
function makeCollapsible(listElement){
// removed list item bullets and the sapce they occupy
listElement.style.listStyle='none';
listElement.style.marginLeft='0';
listElement.style.paddingLeft='0';
// loop over all child elements of the list
var child=listElement.firstChild;
while (child!=null){
// only process li elements (and not text elements)
if (child.nodeType==1){
// build a list of child ol and ul elements and hide them
var list=new Array();
var grandchild=child.firstChild;
while (grandchild!=null){
if (grandchild.tagName=='OL' || grandchild.tagName=='UL'){
grandchild.style.display='none';
list.push(grandchild);
}
grandchild=grandchild.nextSibling;
}
// add toggle buttons
var node=document.createElement('img');
node.src = CLOSED_IMAGE;
node.className = 'collapsibleClosed';
node.onclick=createToggleFunction(node,list);
child.insertBefore(node,child.firstChild);
}
child=child.nextSibling;
}
}
And here's the second function:
function createToggleFunction(toggleElement,sublistElements){
return function(){
// toggle status of toggle gadget
// Use foo.className = 'bar'; instead of foo.setAttribute('class', 'bar');
if (toggleElement.className == 'collapsibleClosed') {
toggleElement.className = 'collapsibleOpen';
toggleElement.src = OPEN_IMAGE;
} else {
toggleElement.className = 'collapsibleClosed';
toggleElement.src = CLOSED_IMAGE;
}
// toggle display of sublists
for (var i=0;i<sublistElements.length;i++){
sublistElements[i].style.display=
(sublistElements[i].style.display=='block')?'none':'block';
}
}
}

Internet Explorer (until version 8, and then only in best standards mode) has a very broken implementation of setAttribute and getAttribute.
It effectively looks something like this:
function setAttribute(attribute, value) {
this[attribute] = value;
function getAttribute(attribute, value) {
return this[attribute];
}
This works fine iif the attribute name matches the property name, and the property takes a string value.
This isn't the case for the class attribute, where the matching property is className.
Use foo.className = 'bar'; instead of foo.setAttribute('class', 'bar');

node.onclick=createToggleFunction(node,list);
That is probably not what you want. Does createToggleFunction return a function? If it doesn't, then I bet you meant this:
node.onClick = function() { createToggleFunction(node, list); };
If my guess is right then the way you have it will set the onClick event handler to be the result of createToggleFunction, not a function like it needs to be.