How to get ID when you pass my ID - javascript

I have a function that gets passed the document object like:
toggle( $('username') );
function Toggle(id)
{
/// ??
}
How can I get the actual name of the object passed i.e. username?

If I understand you correctly, can't you:
$(id).attr("id");
or
$(id).attr("name");
Or am I mistaken?

Either what Jonathon said or with
$(id).val();

The object that gets passed in is an instance of the jQuery object, which contains a set of elements (in this case with only one element in it). The documentation is on the jQuery documentation site.

The jQuery object that $() returns, wraps one or more DOM elements.
Using the accessors $().attr(), $().val(), $().text() and $().html() will act on the first of those wrapped elements.
If you want to drop out of jQuery mode so that you can work with the native DOM element (sometimes useful) use $().get( index ).
eg
var el = $('#mytextbox').get(0);
el.value = 'a new value';
alert(el.id);
etc...

Related

Return jQuery object (instead of DOM) from jQuery array using index

I have a jQuery array of <span>s and I'd like to get just one of them as a jQuery object so that I can string additional methods on it. Something like $mySpans[2] (which returns a string), or $mySpans.get(2), (which returns the DOM element directly).
I know that this will work:
$($mySpans[2]).someJQueryMethod( ... );
...but it seems a little redundant. What is the right way to do this?
Like this:
$myspans.eq(2).method();
jsFiddle Demo
You are going to want to use eq. Note that it will return the jQuery object wrapped element at that index, so if you only have one match you should use 0 (which follows that 2 will return the third of the set).
var $thirdMatch = $mySpans.eq(2);//== jQuery object with third match
var htmlElement = $thirdMatch[0];//== actual dom element
var matchedHtml = $thirdMatch.html();// call some jQuery API method
It is common practice when storing jQuery objects to use a $variableName for readability purposes.

Editing objects in jQuery

$(function(){
var z = document.body.children[0];
var x=$("li", z);
x.name="Johnny";
alert(x.prop(name));
});
x should be an object containing all the elements within the first ul in the body.
Regardless of what the object contains, I would like to add a property with a value, and then use the prop() method to show it - but that doesn't seem to work. Why is that?
I saw a script containing the following: var $x = $("div"); - Do I have to add $ to the variable name if it's a jQuery object?
To select the first ul element inside a page you can do:
$("ul:first li")
This way you are going to select all lines inside the first list in the page.
To store arbitrary data in an element you can use the method data, like this:
$("element").data('key', 'value');
and to retrieve the data:
$("element").data('key');
More info, for the data method.
If you really want to add an attribute you can use the attr method, it works the same way as the data method, but it would reflect in the DOM.
If you want all li elements in the first ul element, then this should do the trick:
var elements = $("ul:eq(0) li");
Here is a very simple example of this in action.
In regards to setting a property, you can do element.name = "test" and it will work ok. But what you need to understand is that this is setting a name property on the jquery collection object and NOT on any of the actual elements.
What you can do however, is set the property like so:
elements.prop("name", "test");
and the access it like so:
var name = elements.prop("name");//name will be "test"
Here is a working example
As I mentioned in my comment, you don't need to prefix the variable with $. But this can be helpful to easily see which variables are JQuery objects.
Number 1. x is a jQuery object, you added to that instance a name property, then you're using name though it wasn't defined.
If you want to change a property of the element you got with jQuery the ways are:
$('selector').prop('property', 'value');
$('selector').attr('attribute', 'value');
$('selector').get(index).property = "value";
Number 2. no you don't have to, $ prefix is simply a convention to make the code more readable.
Is there any specific reason behind using $ with variable in jQuery
Using the selector from #musefan answer, you can take the collection returned, and use the attr() method to add an attribute and value to each item selected. However, I've modified his selector slightly to actually grab "all" elements in there, (just in case future visitors wonder)
var elements = $("ul:eq(0)").children();
elements.attr("attrName", value);
So if you wanted to set the title:
var elements = $("ul:eq(0)").children();
elements.attr("title", "Johnny");
You probably don't want to alert these values, browsers may ask you to stop allowing alerts on the page... but if you really did, then you could throw in an .each() after that.
var elements = $("ul:eq(0)").children();
elements.attr("title", "Johnny").each(function(){
alert($(this).attr("title");
});

Is a Function Argument a Native Element or a jQuery Set?

I'm writing a general purpose helper function in JavaScript. It accesses the className property of the element.
But since I'm using jQuery, it turns out that sometimes the element passed as an argument is actually an array (a jQuery set).
What is the simplest way to use an argument if it's an element or get the first element from the set if the argument is a set? Does jQuery have a tool for this?
You can test if the object is a jQuery object by using instanceof:
if (myObject instanceof jQuery) {
// use $.each to loop over myObject and get class names of all
// or just use myObject[0].className to return only the first
} else {
// it's not a jQuery object
}
You always want a native element? Each jQuery object has a property jquery (containing the jQuery version) so you can use it to check if the element you got is likely to be a jQuery object:
obj = obj.jquery ? obj[0] : obj;
If you are not into ducktyping:
obj = (obj instanceof jQuery) ? obj[0] : obj;
In case you want to pass a single element, an array of elements or a jQuery object to the same method, do the following:
function stuff(element) {
element = [].concat(element)[0];
}
If you have to deal with both jQuery objects and non-jQuery elements, this is a bit tougher. Keep in mind that the jQuery collection can possibly have different classNames for each element, i.e. the first and others may not be the same.
It's slightly inefficient, but this will work:
function (obj) {
var className = $(obj).get(0).className;
}
Wrapping a jQuery object in jQuery() does nothing, but wrapping the element allows you to access it again via .get. It's inefficient because you may have an extra $() call.
If that's no good, you could check obj.hasOwnProperty('className') since a jQuery object usually should not have it, but I think that is riskier.
Is a jQuery Object an Element or an Array of Elements?
Strictly, neither.
A jQuery object is a Javascript object that has some of the Array capabilities. In most aspects you can use it as an array of elements.
If the jQuery object may contain several elements, and you only want the first, you can use the first method to get that:
elements = elements.first();
If the parameter can be either an element, an array of elements, or a jQuery object, you can wrap it in a jQuery object to handle all the cases:
elements = $(elements).first();

Javascript - extract object ID from a Javascript object

So I am not sure if my title is clear enough. I essentially have a div saved as a Javascript object which looks like this: [div#field_30.checkbox_group]
The field_30 is the ID which I am trying to extract here. doing something like object.id is not working. Does anyone know how to get the ID?
Note: I saved the object like this: var object = $(".workspace .selected"); which grabs the currently selected div inside the object called workspace. Sorry is this is a rookie mistake, I just can't seem to find anything anywhere. Thanks for the help...
var object = $(".workspace .selected"); will return a jQuery wrapped element that has jQuery properties and methods rather than element properties and methods. This means that any of
object[0].id
object.prop("id")
object.attr("id")
should work, but the 1st option should be the best performance-wise. It gets the id property of the the 1st element contained by the jQuery object, which is your div.
Your object is in fact a jQuery object, not a dom object.
To use the dom object use,
object[0].id
Or using, jquery, (Since it is already there)
object.prop('id');
You can use either $jquery_object.attr('id') or $jquery_object.eq(0).id
See this for exemple: http://jsfiddle.net/cquuT/
In this case it looks like object is the result of a jQuery select. To get to the actual DOM object you need to use [0]. Then you can access the id property
object[0].id
I don't see a complete answer here, so I'll provide my own.
If you're using jQuery selector $(), then you'll get jQuery-wrapped collection, not a single element.
(I assume now that you're using jQuery 1.5.2, the same as StackOverflow uses now.)
Universal solution to get ids of all elements returned by selector is:
.map(function(){ return this.id; })
Running $(".post-text").map(function(){ return this.id; }) on current page will return something like: ["", "", "", "", ""]
To get id of the first element returned by selector use:
.attr('id')
Running $("div").attr('id') on current page will return "notify-container".
Since jQuery 1.6 you can also use .prop('id') here.
If you know, that query will return only one element or you just want the first element matching given selector, then use .attr which is obviously a simpler solution.

document.getElementById vs jQuery $()

Is this:
var contents = document.getElementById('contents');
The same as this:
var contents = $('#contents');
Given that jQuery is loaded?
Not exactly!!
document.getElementById('contents'); //returns a HTML DOM Object
var contents = $('#contents'); //returns a jQuery Object
In jQuery, to get the same result as document.getElementById, you can access the jQuery Object and get the first element in the object (Remember JavaScript objects act similar to associative arrays).
var contents = $('#contents')[0]; //returns a HTML DOM Object
No.
Calling document.getElementById('id') will return a raw DOM object.
Calling $('#id') will return a jQuery object that wraps the DOM object and provides jQuery methods.
Thus, you can only call jQuery methods like css() or animate() on the $() call.
You can also write $(document.getElementById('id')), which will return a jQuery object and is equivalent to $('#id').
You can get the underlying DOM object from a jQuery object by writing $('#id')[0].
Close, but not the same. They're getting the same element, but the jQuery version is wrapped in a jQuery object.
The equivalent would be this
var contents = $('#contents').get(0);
or this
var contents = $('#contents')[0];
These will pull the element out of the jQuery object.
A note on the difference in speed. Attach the following snipet to an onclick call:
function myfunc()
{
var timer = new Date();
for(var i = 0; i < 10000; i++)
{
//document.getElementById('myID');
$('#myID')[0];
}
console.log('timer: ' + (new Date() - timer));
}
Alternate commenting one out and then comment the other out. In my tests,
document.getElementbyId averaged about 35ms (fluctuating from 25ms up to 52ms on about 15 runs)
On the other hand, the
jQuery averaged about 200ms (ranging from 181ms to 222ms on about 15 runs).
From this simple test you can see that the jQuery took about 6 times as long.
Of course, that is over 10000 iterations so in a simpler situation I would probably use the jQuery for ease of use and all of the other cool things like .animate and .fadeTo. But yes, technically getElementById is quite a bit faster.
No. The first returns a DOM element, or null, whereas the second always returns a jQuery object. The jQuery object will be empty if no element with the id of contents was matched.
The DOM element returned by document.getElementById('contents') allows you to do things such as change the .innerHTML (or .value) etc, however you'll need to use jQuery methods on the jQuery Object.
var contents = $('#contents').get(0);
Is more equivilent, however if no element with the id of contents is matched, document.getElementById('contents') will return null, but $('#contents').get(0) will return undefined.
One benefit on using the jQuery object is that you won't get any errors if no elements were returned, as an object is always returned. However you will get errors if you try to perform operations on the null returned by document.getElementById
No, actually the same result would be:
$('#contents')[0]
jQuery does not know how many results would be returned from the query. What you get back is a special jQuery object which is a collection of all the controls that matched the query.
Part of what makes jQuery so convenient is that MOST methods called on this object that look like they are meant for one control, are actually in a loop called on all the members int he collection
When you use the [0] syntax you take the first element from the inner collection. At this point you get a DOM object
In case someone else hits this... Here's another difference:
If the id contains characters that are not supported by the HTML standard (see SO question here) then jQuery may not find it even if getElementById does.
This happened to me with an id containing "/" characters (ex: id="a/b/c"), using Chrome:
var contents = document.getElementById('a/b/c');
was able to find my element but:
var contents = $('#a/b/c');
did not.
Btw, the simple fix was to move that id to the name field. JQuery had no trouble finding the element using:
var contents = $('.myclass[name='a/b/c']);
var contents = document.getElementById('contents');
var contents = $('#contents');
The code snippets are not the same. first one returns a Element object (source).
The second one, jQuery equivalent will return a jQuery object containing a collection of either zero or one DOM element. (jQuery documentation). Internally jQuery uses document.getElementById() for efficiency.
In both the cases if more than one element found only the first element will be returned.
When checking the github project for jQuery I found following line snippets which seems to be using document.getElementById codes (https://github.com/jquery/jquery/blob/master/src/core/init.js line 68 onwards)
// HANDLE: $(#id)
} else {
elem = document.getElementById( match[2] );
Just like most people have said, the main difference is the fact that it is wrapped in a jQuery object with the jQuery call vs the raw DOM object using straight JavaScript. The jQuery object will be able to do other jQuery functions with it of course but, if you just need to do simple DOM manipulation like basic styling or basic event handling, the straight JavaScript method is always a tad bit faster than jQuery since you don't have to load in an external library of code built on JavaScript. It saves an extra step.
One other difference: getElementById returns the first match, while $('#...') returns a collection of matches - yes, the same ID can be repeated in an HTML doc.
Further, getElementId is called from the document, while $('#...') can be called from a selector. So, in the code below, document.getElementById('content') will return the entire body but $('form #content')[0] will return inside of the form.
<body id="content">
<h1>Header!</h1>
<form>
<div id="content"> My Form </div>
</form>
</body>
It might seem odd to use duplicate IDs, but if you are using something like Wordpress, a template or plugin might use the same id as you use in the content. The selectivity of jQuery could help you out there.
All the answers are old today as of 2019 you can directly access id keyed filds in javascript simply try it
<p id="mytext"></p>
<script>mytext.innerText = 'Yes that works!'</script>
Online Demo!
- https://codepen.io/frank-dspeed/pen/mdywbre
jQuery is built over JavaScript. This means that it's just javascript anyway.
document.getElementById()
The document.getElementById() method returns the element that has the ID attribute with the specified value and Returns null if no elements with the specified ID exists.An ID should be unique within a page.
Jquery $()
Calling jQuery() or $() with an id selector as its argument will return a jQuery object containing a collection of either zero or one DOM element.Each id value must be used only once within a document. If more than one element has been assigned the same ID, queries that use that ID will only select the first matched element in the DOM.
All the answers above are correct. In case you want to see it in action, don't forget you have Console in a browser where you can see the actual result crystal clear :
I have an HTML :
<div id="contents"></div>
Go to console (cntrl+shift+c) and use these commands to see your result clearly
document.getElementById('contents')
>>> div#contents
$('#contents')
>>> [div#contents,
context: document,
selector: "#contents",
jquery: "1.10.1",
constructor: function,
init: function …]
As we can see, in the first case we got the tag itself (that is, strictly speaking, an HTMLDivElement object). In the latter we actually don’t have a plain object, but an array of objects. And as mentioned by other answers above, you can use the following command:
$('#contents')[0]
>>> div#contents

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