I am not very sure with the use of "this" [current context] in jquery.What I know is- it prevents the dom from searching all the elements, it just work on that current element, which improve performance[correct me if I am wrong].Also I am not sure when to use this and when not.
lets say, should I go for
$("span",this).slice(5).css("display", "none")
or
$("span").slice(5).css("display", "none")
both will work, but I am not very clear as how really it works.can somebody explain it with a diff/proper example, and when to use what?
[EDIT]
$(function() {
$("#clickme").click(function() {
$("span",this).slice(5).css('display', 'block');//doesn't work ? why?
$("span").slice(5).css('display', 'block');//works..why?
});
});
enter code here <span id="clickme">Click me</span>
<span>itam1</sapn>
<span>itam2</sapn>
<span>itam3</sapn>
<span>itam4</sapn>
<span>itam5</sapn>
...upto10
Usually you can use the this keyword on event handlers since it will be a reference to the element that triggered the event and other jQuery functions like $.each.
For example when handling a click event lets say:
$('.parentElement').click(function () {
$('.foo', this).hide();
});
The above code, will hide all the elements with class foo that are descendants of the currently parentElement that was clicked.
The use of the context argument of the jQuery function is the equivalent of making a call to the find method:
$(expr, context);
// is just equivalent to:
$(content).find(expr);
EDIT: Looking at your example:
$("#clickme").click(function() {
$("span",this);//... (1)
$("span");//.. (2)
});
The first line, will look for all the span elements that are inside of #clickme (its descendants), since that element was the one that triggered the click event.
The second line, will look for all the span elements on the whole page.
How it works
Lets use this HTML for the examples:
<div id="container">
<div class="column">Link 1</div>
<div class="column">Link 2</div>
</div>
<div id="footer">
Link 3Link 3
</div>
The scoping parameter of the jQuery function should only be used if you already have a cached reference to a DOM element or jQuery wrapped element set:
var $set = $('#container');
$('a', $set).hide(); // Hides all 'a' tag descendants of #container
Or in an event:
$("#container").click(function(e){
$('a', this).hide(); // Same as call above
}
But it makes no sense to use it like this:
$('a', '#container').hide()
When it should be written like this:
$('#container a').hide();
Having said all that, it is generally cleaner and clearer to just use .find() instead of using the second parameter in the jQuery function if you already have the jQuery or DOM element. The first example I gave would be written this way instead:
var $set = $('#container');
$set.find('a').hide(); // Hides all 'a' tag descendants of #container
If this one call was the only reason you grabbed the #container object, you could also write it this way since it will still scope the search to the #container element:
$("#container a").hide(); // This is the same as $('a', "#container");
Why would you scope your selections
When jQuery looks for an unscoped selector, it will search through the entire document. Depending on the complexity of the selector, this could require a lot of searching. If you know that the element you are looking for only occurs within a specific parent, it will really speed up your code to scope the selection to that parent.
Regardless of what method of scoping you choose, you should always scope your selectors whenever possible.
Related
On a web page we have a list of profiles. On the right hand side of the profile is some text, followed by an arrow img#arrow.
When img#arrow is clicked, we have the following jQuery we hope to run:
However, the corresponding .bottom-sec is not toggling.
jQuery('#arrow').click(function(){
var $parent = $(this).parent();
$($parent).addClass('active');
jQuery($parent +' .bottom-sec').toggle();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="profile-right">
<h2>Bob Brown</h2>
<h3>Non-Executive Chairman</h3>
<p>Intially showing text.</p>
<div class="bottom-sec" style="display: none;">
<p>Initially hidden text.</p>
</div>
<img id="arrow" src="/wp-content/themes/wtc/images/icons/down-arrow-circle-hi.png">
</div>
Problem
The problem with your code is exactly what the comment on your question is saying, but he didn't explain anything:
You're combining two different ways of selecting elements. One is with selectors, the other is traversing. You're using them in a way which isn't possible (the $parent + ' .bottom-sec' part). The comment linked to a jQuery page about traversing which you should definitely read! It tells you a lot about how to use traversing functions, which you could use!
Solution
There are multiple solutions to this, but I'll write down the one I think is the best:
First of all, change the HTML a bit. I've removed the element style of .bottom-sec and changed the id of the image to a class, because you have multiple images with the same id on the page, which is not a recommended thing to do. Classes can occur more than once, id's cannot.
<div class="profile-right">
<h2>Bob Brown</h2>
<h3>Non-Executive Chairman</h3>
<p>Intially showing text.</p>
<div class="bottom-sec">
<p>Initially hidden text.</p>
</div>
<img class="arrow" src="/wp-content/themes/wtc/images/icons/down-arrow-circle-hi.png">
</div>
I've reduced the JavaScript to the following. Note that is just reduced to one line, where a click on the .arrow element goes searching for the closest .profile-right parent. If, for whatever reason, you decide to change the HTML and the .arrow element is no longer a child of the .profile-right, this code still works. The only thing it does is toggle an active class on the .profile-right.
jQuery(document).on('ready', function() {
jQuery('.arrow').on('click', function(){
jQuery(this).closest('.profile-right').toggleClass('active');
});
});
The document ready listener was added because of OP's comment.
With CSS, we can use the new .active class to show or hide the element.
.profile-right .bottom-sec {
display: none
}
.profile-right.active .bottom-sec {
display: block
}
Original Code Fix
If for some reason you wanted to use your original code, this is how it should be:
// Nothing wrong about this part.
// Your only worry should be that there could be
// multiple elements with the same ID, which is something really bad.
jQuery('#arrow').click(function(){
// This part is correct, no worries
var $parent = $(this).parent();
// Removed the $(...), because $parent is already a jQuery object
$parent.addClass('active');
// Changed the selector to a find function
$parent.find('.bottom-sec').toggle();
});
You could also combine all of the code inside the listener function to just one line:
jQuery('#arrow').click(function(){
$(this).parent().addClass('active').find('.bottom-sec').toggle();
});
Change your js code like below.
jQuery('#arrow').click(function(){
var $parent = $(this).parent();
$($parent).addClass('active');
jQuery($parent).find('.bottom-sec').toggle();
});
In your event listener you can catch the element (the down arrow) that triggered the event. It will be referred as this.
Then you can go through the DOM tree using .next() and .parent() to access the <div> to toggle.
Note: you may need more functions than the one I explained above.
Note 2: without code or more detailed information, we can't help you further, I will edit this answer if you add details.
I am very new to Javascript/JQuery and I am going through the code of a colleague of mine. He has created the very common "FAQ" list on a website where the answer is not immediately displayed, only the question until the user clicks the arrow, it then shows the answer.
I am trying to figure out how he got this to work. I understand all the HTML and the CSS (it looks fine), but I can't seem to understand how to get the Jquery to work or where to call the code when the user press the arrow on the question to display the answer.
The code he seemed to use is at the bottom. Once again, all the HTML and CSS is linked up so I think it is a matter of simply how to use the code.
If anyone can offer any help, that would be appreciated.
Thanks!
$("#faq").on("click", "div > a", function() {
return $(this).next().toggle().closest("li").toggleClass("arrow_up"), !1
})
Let me annotate his code for you. It uses some shorthand that can be a little confusing for beginners.
// Select the element with an id attribute of "faq".
// When an <a> which is a first-level child of a div inside of
// #faq is clicked, perform the following actions
$("#faq").on("click", "div > a", function() {
// "this" references the <a> tag.
// $(this) wraps it in a jQuery wrapper
return $(this)
// get the next sibling of the <a>. It is our <p>
.next()
// switches the element.style.display between none and block
.toggle()
// get the nearest parent <li> element.
.closest("li")
// add or remove the arrow_up CSS class
.toggleClass("arrow_up"), !1 // !1 is a shortcut for false
});
I have a full distilled and annotated reproduction in this jsFiddle link
He also uses a shorthand for return false as well. Notice that the body of his event handler is all on one line. He could have split it into two lines, but he used the comma operator to make it fit on just one.
$(this).next().toggle().closest("li").toggleClass("arrow_up");
return false; // false === !1;
Returning false from a jQuery event handler prevents the event from reaching parent elements in the DOM.
That means:
//Bind a click function on every a tag in #faq
$("#faq").on("click", "div > a", function() {
// Toggle Class (so if the closest <li> Element has class "arrow_up" then remove it, otherwise add it)
return $(this).next().toggle().closest("li").toggleClass("arrow_up"), !1
Check out here for Example "Bootstrap Collapse" which is exactly the same you are looking for:
http://getbootstrap.com/javascript/#collapse
There is also a Demo Code provided and you see how to handle that.
I've been using jQuery for a while but this is a new one. A simplified example:
HTML
<div class='custom'></div>
<div class='custom'></div>
<div class='custom'></div>
jQuery:
var $customElems = $('.custom'),
$spanOuter = $('<span class="outer"/>'),
$spanInner = $('<span class="inner"/>');
$customElems.each( function() {
$(this).wrap($spanOuter).after($spanInner);
});
JSFiddle:
http://jsfiddle.net/a3ZK8/
I would have expected the 'inner' span to be added to all three elements in the selection but it gets always inserted into the last one only (no matter how many). I tried it with .before(), with and without the chaining, same result. What am I missing??
The problem is you are using a reference to a jQuery object.
Hence you keep moving the object reference around within each iteration.
If you have no events attached or no need for the span to be a jQuery object then just pass the parameter as a HTML string literal instead of an object reference
Cloning a jQuery object that doesn't need to be a jQuery object in the first place is just redundant processing and unnecessary overhead.
Change your jQuery object to a string similar to this:
spanInnerString = '<span class="inner"/>';
and your method like this:
$(this).wrap($spanOuter).after(spanInner);
The result is:
<span class="outer"><div class="custom"></div><span class="inner"></span></span>
<span class="outer"><div class="custom"></div><span class="inner"></span></span>
<span class="outer"><div class="custom"></div><span class="inner"></span></span>
DEMO - Passing parameter as HTML string
Off course, the same goes for the outer span. Don't create jQuery objects unless you have to.
If you must use a jQuery object because you want to attach events to the span or similar, than cloning is the way to go, though make sure you use clone(true, true) then to also clone the attached events.
You need to clone the element. Otherwise, after() will relocate the same element 3 times, which results in it being attached to only the last looped element.
$customElems.each(function () {
$(this).wrap($spanOuter).after($spanInner.clone());
});
Demo: Fiddle
You might ask, "Why would wrap() work?" That's because 'wrap()' internally clones the element.
You're moving the same span from place to place. If you acted on all three divs at once, jquery will instead clone the span.
http://jsfiddle.net/a3ZK8/1/
var $customElems = $('.custom'),
$spanOuter = $('<span class="outer"/>'),
$spanInner = $('<span class="inner"/>');
$customElems.wrap($spanOuter).after($spanInner);
From the documentation for .after:
Important: If there is more than one target element, cloned
copies of the inserted element will be created for each target except
for the last one.
which means the last element will always get the original, while all other selected elements will get a clone. That's why when you acted on one element at a time, it simply moved the same span around.
This question is connected with that
This code hides div when user type data to inputs and focus on another div
$(".Q,.A").blur(function(e) {
if ($(this).val().length > 0 && $(this).siblings("input").val().length > 0) {
$(this).parent().fadeOut(1000);
getData("ajaxPHP/insertNewWords.php?q='" + $(this).siblings('input').val() + "'&a='" + $(this).val() + "'&zestawID="+zestawID, "console");
$(".main").append("<div><input type='text' class='Q'></input><input type='text' class='A'></input></div><br>");
}
});
And when user enter data, this div hides and script creates new div (so user can enter infinite amount of data).
The problem is: new created divs don't hide.
So what should I do, if I want to involve new created divs into "$(".Q,.A")"?
The problem is (as I understand it), that you have a behaviour attached to a set of nodes on your page, and new nodes added to the page do not pick up this behaviour.
This is because of the way JQuery works. When you define a selector like $(".Q,.A") this selector evaluates to a set of known nodes on your page. The code that follows only applies to those found elements. This selector is never evaluated again, so any new nodes never get a chance to gain your desired behaviour.
The solution is to get JQuery to re-evaluate the selector every time the event occurs. So you need to listen for the event globally, then filter to only handle the elements that match your selector.
The correct way to do this is on
$(document).on("blur", ".Q,.A", function(){ ... });
See: http://jsfiddle.net/sAT6L/
Live has some discussion on how it used to be done in each version of JQuery.
Note: You should be able to restrict the scope to something more local than $(document).
You can use jquery's .on method on the parent container, because events "bubble" to the parent container. The on function also allows you to specify a selector to filter the children elements, which gets applied dynamically, so you can use your ".Q,.A" selector there:
$(document).ready(function(){
$("#container").on("blur", ".Q,.A", function(e){
if($(this).val().length>0 && $(this).siblings("input").val().length>0){
$(this).parent().fadeOut(1000);
$("#container").append('<div><input type="text" class="Q"><input type="text" class="A"></div>');
}
});
});
Fiddle: http://jsfiddle.net/rK3HS/1/
Here's how I append the value:
$('<div>someText</div>').appendTo(self);
And here's how I want to remove it:
$(self).remove('<div>someText</div>');
The appending works, the removing doesnt. What am I doing wrong?
The .remove() function takes a selector to filter the already matched elements, not to match elements inside of them. What you want is something like this:
$(self).find('div:contains(someText)').remove();
That will find a <div> element containing the text someText inside of whatever element self is, then removes it.
The API http://api.jquery.com/remove/ sais that a selector is required.
Try $(self).remove('> div');
This will remove the first childs of div.
You can use $(self).filter('div:contains("someText")').remove(); to remove a div with a specific content or $(self).find('> div').remove(); to remove the first childs of div.
EDIT: removed first version I posted without testing.
It most likely has to do with the scope of self. Since you've named it self I am assuming that you are getting this variable using $(this) on the click event. If that's the case, and you want to call the remove method, you can only do so from within the same function. Otherwise you need to either store the element in a variable or provide another selector to access it.
Example:
<div class="div1"></div>
this will be the div with the click event
$(document).ready(function(){
var self = null;
$('.div1').click(function(e){
self = $(this);
var itemToAdd = '<div>SomeText</div>';
$(itemToAdd).appendTo(self);
});
// to remove it
// this will remove the text immediately after it's placed
// this call needs to be wrapped in a function called on another event
$('.div1').find('div:contains(someText)').remove();
});