I am trying to write a short script that looks to see if a class or id is present in then document. If it is then do the following:
$(".tab_item").removeClass("tab_item_color");
$(this).addClass("tab_item_color");
You can use the length property on a jQuery object. For example:
if( $('.your-class').length )
{
$(".tab_item").removeClass("tab_item_color");
}
The if() block will only execute if there is an element in the DOM which has a class of your-class.
You can also do this
$(function() {
if ($('.yourClassName').length){
$(".tab_item").removeClass("tab_item_color").addClass("YourNewClassName"); //It will swap your class.
}
});
For more information you can also visit .length
You can simplify this by checking the first object that is returned from jquery. For-example
if ($(".your-class")[0]){
$(".tab_item").removeClass("tab_item_color");
}
Related
I am trying to use javaScript to determine if an element with a specific class name exists on an html page. The element in question is only sometimes loaded on the page.
When I use document.getElementsByClassName('element-in-question').innerHTML = "Hello"
It will work when the element exists, but when it doesn't exist, it will return as "cannot set property of innerHTML of undefined and the rest of the code will not run.
Is there a way to check if an element exists, and only modify it when it does without breaking the rest of the code?
Thanks for the help
You can also use document.querySelector which will return the first element within the document if it exists, if not, it returns null.
const targetElement = document.querySelector('.element-in-question');
if (targetElement) {
targetElement.innerText = 'Hi there!';
}
<div class="element-in-question"></div>
Tip: If you're just adding text consider using innerText instead of innerHTML.
Just wrap you code with if statement :
const elemts = document.getElementsByClassName('element-in-question');
if(elemts.length) {
// this actually need to be elemts[0].innerHTML
elemts.innerHTML = "Hello"
}
Note: document.getElementsByClassName will return array/collection of elements so if you really know that there is no other elements keep using it otherwise switch to getElementById.
as per documentation:
The getElementsByClassName() method returns a collection of all
elements in the document with the specified class name, as an
HTMLCollection object.
It's very simple with the condition IF
If you want to get elements by class, the function will return an array (a collection of all elements in the document with the specified class name), so you will check as following :
if (document.getElementsByClassName('class-in-question').length > 0) {
// Existed
}
If you want to get an element by specified id, the function will return an objet HTML with that id, so you will check as following :
if (document.getElementById('id-in-question')) {
// Existed
}
I am trying to perform an action to other elements than the $(this) item
$('.items').click(function(){
var myitem = $(this);
$(".items").each(function() {
if (myitem == $(this)){
break;
} else {
//perform action
}
});
});
Where did I go wrong? Is there any better method?
Try to use the .not() function to filter out the current element,
$('.items').click(function(){
$('.items').not(this).each(function(){
//perform action here.
});
});
What went wrong?
When using the jQuery method (a.k.a. $) a new instance of the jQuery object is created, containing a list of elements matching your selector along side with a rich prototype of jQuery's methods.
Your mistake was to try and compare two different instances.
What you could have done was to compare the elements themselves by making the following changes:
// change this:
var myitem = $(this);
// to this:
var myitem = this;
// change this:
if (myitem == $(this)){
// to this:
if (myitem == this){
Unless you intend to use the jQuery object functionality there's no reason to initiate a new instance. Simply use the element itself when possible. It's a best practice to avoid such use cases. Performance wise.
Best solution
But the best solution in your case is what was mentioned in all other answers, using jQuery's not method to exclude the element from the newly created instance.
Using.not() to avoid
Try this
$(".items").not($(this)).each(function() {
});
OR
As per your code
$(".items").not(myitem).each(function() {
});
you can use not() to ignore the element which is clicked:
$(".items").not(this).each(function() {
});
I'm having a bit of a brain fart here, and hoping someone can help me find a 1-line solution to this problem, without having to call .each().
So I get a list of all checkboxes within a container like this:
var checkboxes = $(':checkbox', '#surveyModal');
At some point later, I need to find out if any (or none) of the checkboxes are checked within that list.
I expected something like these to work:
$(':checked', checkboxes)
// or
checkboxes.attr(':checked')
// or
$(checkboxes).attr(':checked')
But it doesn't. The only thing I've had success with is calling each() and then checking each individually. But that means I'll have to keep a separate variable (.e.g. someAreChecked at a higher-level scope, which I don't feel is optimal.
checkboxes.each(function () {
if ($(this).attr('checked')) {
someAreChecked = true;
}
});
I was hoping that I can easily in a single line do such a check:
if (checkboxes.('get checked count') == 0)
{
}
Thanks in advance.
The filter function is what you're looking for :)
checkboxes.filter(':checked').length;
.attr returns the value of an attribute, and you have to pass the attribute's name to it, not a selector.
Just use .is instead.
Description: Check the current matched set of elements against a
selector, element, or jQuery object and return true if at least one of
these elements matches the given arguments.
$(checkboxes).is(':checked')
This should do it:
$("input[type=checkbox][checked]").length
I am trying to attach an onChange callback to all the input elements under the div #dim. It selects all 3 input elements, but returns an exception:
Uncaught TypeError: Object 0 has no method 'change'
It may be because x may not be a jQuery object. How would I make this work?
function registercb() {
var sel = $("div.dim > input");
for (x in sel) {
x.change(function() {
dosomething();
});
}
}
You can simply do:
function registercb() {
$("div.dim > input").change(dosomething);
}
A few things to watch for:
Inside that iteration (don't use this, see the next point) x is the DOM element, not a jQuery object which has the .change() method, you would need to wrap it in a jQuery object like $(x), but again that isn't the correct solution here.
Don't use a for(...in...) loop to iterate an object (a jQuery object is array-like), that type of loop is for enumeration.
Most jQuery functions (almost all) run on more than one element, so just run it on the set to affect all elements, .change() is one of these.
In the cases you do need to loop, check out .each(), as it'll make your life much easier, don't use this here, it's only an example of what it would look like:
Example:
function registercb() {
$("div.dim > input").each(function() {
$(this).change(dosomething);
});
}
You don't have to loop over the elements. You can think of a jQuery object as holding a collection. When you do:
var sel = $("div.dim > input");
It means that sel has all the input elements in it, so then when you run a method like change() it will affect all of the elements in the collection. Thus you can do something like this:
function registercb() {
$("div.dim > input").change(function(){
dosomething();
});
}
Bonus knowledge: Now your problem is that when you were doing for( x in sel ) you are getting a lot of stuff on the jQuery object itself that you don't want. If you run the following code in chrome you'll see it outputting a lot unexpected stuff:
for( x in sel ){
console.log( x );
}
Instead jQuery has the each that lets you loop over the things you want:
sel.each(function(index, item){
console.log(item);
});
You can even use it on other things, which is really handy!
$([1,2,3]).each(function( index item ){
console.log( item ); // 1,2,3
})
Assuming your 'dim' div has an ID rather than a class of dim, you can simply do this:
$("#dim > input").change(function() { dosomething(); });
Working example.
In the text you refer to #dim whereas in the code you're refering to .dim - # selects by ID and . selects by class, so if your div is in the format <div id="dim"> then you won't find any matched elements with div.dim as your selector.
This question already has answers here:
Is there an "exists" function for jQuery?
(47 answers)
Closed 8 years ago.
How do I check if an element exists if the element is created by .append() method?
$('elemId').length doesn't work for me.
$('elemId').length doesn't work for
me.
You need to put # before element id:
$('#elemId').length
---^
With vanilla JavaScript, you don't need the hash (#) e.g. document.getElementById('id_here') , however when using jQuery, you do need to put hash to target elements based on id just like CSS.
Try to check the length of the selector, if it returns you something then the element must exists else not.
if( $('#selector').length ) // use this if you are using id to check
{
// it exists
}
if( $('.selector').length ) // use this if you are using class to check
{
// it exists
}
Try this:
if ($("#mydiv").length > 0){
// do something here
}
The length property will return zero if element does not exists.
How do I check if an element exists
if ($("#mydiv").length){ }
If it is 0, it will evaluate to false, anything more than that true.
There is no need for a greater than, less than comparison.
your elemId as its name suggests, is an Id attribute, these are all you can do to check if it exists:
Vanilla JavaScript: in case you have more advanced selectors:
//you can use it for more advanced selectors
if(document.querySelectorAll("#elemId").length){}
if(document.querySelector("#elemId")){}
//you can use it if your selector has only an Id attribute
if(document.getElementById("elemId")){}
jQuery:
if(jQuery("#elemId").length){}
You can also use array-like notation and check for the first element.
The first element of an empty array or collection is simply undefined, so you get the "normal" javascript truthy/falsy behaviour:
var el = $('body')[0];
if (el) {
console.log('element found', el);
}
if (!el) {
console.log('no element found');
}
You can use native JS to test for the existence of an object:
if (document.getElementById('elemId') instanceof Object){
// do something here
}
Don't forget, jQuery is nothing more than a sophisticated (and very useful) wrapper around native Javascript commands and properties
If you have a class on your element, then you can try the following:
if( $('.exists_content').hasClass('exists_content') ){
//element available
}