I create an object in my javascript function, and I'd want to retrieve it in c++ from dom class for change some values, but I can access only by id, tag or class that are part of css syntax. Is there the possibility to get my object and set values or send to him those value?
First of all I think you should always get DOM elements by id or class name because IMHO it's the most versatile way to get things from this kind of tree.
Anyway, just like any other DOM Minko provides the childNodes and parentNode properties if you want/have to browse the tree :
AbstractDOM::childNodes()
AbstractDOM::parentNode()
When you've found the right DOM element, you can then use the other DOM methods to get its content, set its value, etc... Everything you need should be in the AbstractDOM base class definition.
Related
I've read the this and this, but I'm trying to figure out how document.getELementbyClassName works so that I can re-implement it as an exercise. Obviously, I don't wan to just imitate the source code; my version will probably be much slower and more crude. I have a few questions, but any insight provided beyond my questions is appreciated.
When called on the document object, the complete document is searched, including the root node.
How does it search the entire document? Does this use some sort of regular expression?
document.getElementsByClassName('red test'); This is supposed to return all elements that have both red and test classes. But doesn't each element only have one class? Or is this to mean something like red orange test?
Is it correct that the elements are returned in an array? Something like [element1, element2, ...]. I'm not sure what is meant by "array-like."
Note: I'm new to JavaScript and have even less exerpeince with HTML, CSS, and jQuery.
To answer your questions:
Probably recursively. Otherwise there are plenty of different ways to traverse n-ary trees which is what the DOM is. Depth-first, breadth-first, however-you-want-first-really, they can all be implemented recursively, or alternatively use some data structure like a stack or a queue. How it does it really isn't important, what matters is how YOU think it should be done.
A simple algorithm for recursively identifying elements with those classes would be something like this
getByClassName(class, root) {
ret = []
if (root has class) {
ret.push(root);
}
for (each child of root) {
append getByClassName(class, child) to ret;
}
return ret;
}
Elements can have multiple classes. <a class="foo bar baz"> has classes foo,bar, and baz
All the Javascript methods like this operate on the DOM, not the HTML source code. When the HTML is loaded, the browser parses the HTML into the DOM, which is a data structure containing objects that represent the document contents. So it doesn't need to do pattern matching, it simply searches through the data structure for elements whose class list contains the specified class.
ELements can have more than one class, and this is very common. For instance, you might have a button class for all buttons, and an active class for active elements. The active button might then be <span class="button active">contents</span>.
The elements are returned in an HTMLCollection. This is an array-like object, so you can use elements.length to get the number of elements, and elements[i] to access a specific element in the collection. It's also a "live" collection, which means that if you change the DOM, the collection will automatically be updated to reflect the changes (e.g. if you remove the class from the object, it will no longer be in the collection).
Ok so I finally have a code example to show this!
if ($('#Snowsports-row')[0].classList.contains("hidden") == false) {
$('#snowsports-only').removeClass("hidden")
}
The code works ONLY as written above, i.e., if the [0] were moved to the second line and removed from the first line, or if it were present/absent in both lines, it would fail.
I understand the output difference...
$('#Snowsports-row')
=> [<div>...]
$('#Snowsports-row')[0]
=> <div>...
...but I'm not understanding under what circumstances you're OK to get an array of element(s) and in which you need to tease out the exact element.
THANKS FOR ALL ANSWERS! Very clearly helped me to figure out that the problem may have been confusing JS/jQuery methods. Final version:
if ($('#Snowsports-row').hasClass("hidden") == false) {
$('#snowsports-only').removeClass("hidden")
}
The .classList method is not widely supported (not in MSIE 9.0 for example) so it's not portable, although where it exists it's fast.
Since every ID in a document is supposed to be unique, and since calling removeClass for a class that isn't present is harmless, just replace your entire call with:
$('#Snowsports-row').removeClass('hidden')
Or better yet, if that class means what I think it does, use .hide() and let jQuery do its job for you, potentially animation the transition in the process.
Alternatively, if you actually wanted to stick with using DOM and classList, you should use the .remove() method that classList already supports:
document.getElementById('#Snowsports-row').classList.remove('hidden')
although there's a minor disadvantage in that this code will crash if that element isn't found (since .getElementById will return null) whereas jQuery silently ignores calls made on empty selectors.
As for the meta-question - you use [n] if you want to access the single DOM element at position n within the jQuery object, as you've done when you use .classList.
You use .eq(n) to obtain a jQuery object representing that DOM element, e.g. if you want to apply jQuery methods to that (single) element.
If there's only a single element, or you want the jQuery method to apply to every matching element, just call the method directly on the selector, as I've done above.
First off, by using jQuery for what it's good at, you can replace this:
if ($('#Snowsports-row')[0].classList.contains("hidden") == false) {
$('#snowsports-only').removeClass("hidden")
}
with this:
$('#Snowsports-row').removeClass("hidden");
Your first block of code does the following:
With $('#Snowsports-row'), make a jQuery object that contains all DOM elements that match the select '#Snowsports-row'.
Then reach into the jQuery object with [0] and get the first DOM object in that jQuery object.
Then, use a property/method on that DOM element to determine if a class exists on that DOM element with your .classList.contains("hidden") reference.
Then, if you find that class, remove it.
A jQuery object contains inside it an array of DOM elements. If you call a method on the jQuery object itself like:
$('.tableRows').html("hello");
Then, you are asking jQuery to operate on ALL the DOM elements inside the jQuery object. You must use jQuery methods, not DOM methods.
If, on the other hand, you want to use a method such as .classList.contains(), that is only a method on an actual DOM element. That isn't a jQuery method. So, you have to reach inside of the jQuery object to get a specific DOM element out of it. That's what the [0] does. It reaches into the jQuery object and gets the first DOM element from its internal data structure. Once you have that DOM element, you can then use any DOM element methods on that DOM object.
FYI, if you ever want to get just the first DOM element from a jQuery object, but want the result to be a jQuery object, not just a DOM element, instead of [0], you can use .eq(0) like ths:
$('#Snowsports-row').eq(0).removeClass("hidden");
Now, in this specific case, this is never necessary because $('#Snowsports-row') cannot ever contain more than one DOM element because internally jQuery will only return the first matching DOM element when you are searching for a ID value (since there's never supposed to be more than one matching element with the same ID).
Just keep in mind that DOM element and a jQuery object are completely different types of objects with different methods on them. What makes it slightly confusing is that a jQuery object contains an internal list of DOM elements. But, if the object you are operating on is a jQuery object, then you can only call jQuery methods on it. If you reach into the jQuery object and pull out a DOM element, then you can only call DOM methods on it.
First of all, ids must be unique, so if you have more than one #Snowsports-only elements you can experience problems.
In your question, you are mixing jQuery code with pure Javascript code.
This:
if ($('#Snowsports-row')[0].classList.contains("hidden") {
...
}
Means that you get the first instance of #Snowsports-row (remember that is better if there is only one element with this id), but you get the DOM object (pure javascript) with the jQuery selector. You can do the same thing in jQuery like this:
$('#Snowsports-row').hasClass("hidden")
See more:
https://api.jquery.com/hasclass/
https://developer.mozilla.org/es/docs/Web/API/Element/classList
Sure, because you are operating over a list. Now, you're kind of mistaking the jQuery/javascript code. If you would like to use the same line twice you can basically drop jQuery altogether and write something like this:
var el = document.getElementById('Snowsports-row');
if (el.classList.contains('hidden')){
el.classList.remove('hidden');
}
In the first line you're selecting one specific DOM element, whereas in the second line you are selecting ALL elements in the DOM that fit that selector and removing the "hidden" class from all of them. Basically checking whether the element has a class can only be performed over an element (that's why you need to select the index, specifying a given element), but jQuery allows you to remove the class of every element inside a list (hence your second line)
Use jQuery's .eq() function. So:
var el = $('#Snowsports-row').eq(0);
if (el.hasClass("hidden")) {
$(el.removeClass("hidden")
}
There's also no harm in calling removeClass on an element that might not have that class... so:
$('#Snowsports-row').eq(0).removeClass('hidden');
I have some function that recieves javascript object "element" (there is no id speicified for it like id=".."). This js object is already created in DOM and is seen on the page.
For different reasons I am not able to change the object "element" before it comes to the function.
I need to add a new element before given object. I know that this can be done using jquery, but in this case I do not know how to convert javascript to jQuery (if this is possible).
Are there other options how to add element before given js element in DOM?
You are looking for the insertBefore method:
https://developer.mozilla.org/en-US/docs/Web/API/Node.insertBefore
Usage:
function myInsert(element, before) {
before.parentNode.insertBefore(element,before);
}
Would like to maintain a map/hash of DOM objects. Can they serve as key objects? If not, what are the alternatives, please? If there are better ways - kindly enlist them as well.
You can put anything as the key, but before actual use it is always converted to string, and that string is used as a key.
So, if you look at what domObject.toString() produces, you see it is not a good candidate. If all of your dom objects have an id, you could use that id.
If not, and you still desperately need a key based on DOM object, you probably could do with using, for example, _counter attribute with automatic counter in background putting new unique value in a DOM object if _counter is not yet present.
window already maintains all DOM objects as properties. Instead of putting your own keys for each 'DOM object' try to use window or document object and methods that uses index based on the layout of DOM tree.
No, because object keys are strings.
You'd have to "serialise" your objects by id or something, then perform a lookup later. Probably not worth it, depending on what your actual goal is here.
No, but you can set an attribute on the DOM element that contains a number, which you would have as the index in a numerically-indexed array.
Easiest is to set a data-attribute on the element instead.
Not exact. But I think you want something like below. You can do with jquery,
The .serializeArray() method creates a JavaScript array of objects, ready to be encoded as a JSON string. It operates on a jQuery object representing a set of form elements. The form elements can be of several types
Refer below link :
http://api.jquery.com/serializeArray/
So I'm trying to add attributes to a radio button input, specifically the name attribute in Javascript. I'm appending children to a main object and when I use Object.setAttribute("name", value); and subsequently check the innerHTML of the appended input, it does not even contain a name property at all!
I'm guessing I'm missing something simple or there is a way around it but I've been wrestling with this problem for quite a while with no success. I tried accessing the property directly using Object.name = value and Object.nodeName = value (that one was a random try).
Is there some sort of problem in which IE6's javascript rendering engine does not recognize setAttribute("name", value)? Is there a way around it?
Here's a workaround for dealing with IE:
http://javascript.about.com/library/bliebug2.htm
http://www.thunderguy.com/semicolon/2005/05/23/setting-the-name-attribute-in-internet-explorer/
Essentially, the method used is to create the elements on the fly instead of modifying existing elements.
In IE, you cannot add a name attribute on dynamically created objects.
I suggest using id if unique, or a class if not.