Javascript focus() and select() quirk - javascript

Im working on a form and getting null or not an object errors in ie.
<form action="#" method="post" name="adv_search">
<input class="inputbox" type="text" name="keyword1" value="none" id="keyword1"/>
</form>
<script>
document.adv_search.keyword1.focus();
document.adv_search.keyword1.select();
</script>
//whereas if I use
<script>
var key1 = document.getElementById('keyword1');
key1.focus();
key1.select();
</script>
//everything is fine
i would like to understand why.
i would like it to work without having the id tag for the input field
thanks in advance
shouldnt the document.formname.fieldname.focus();
and document.formname.fieldname.select();
work?

Your particular example works for me, but if I add another field with the same name:
<input type="text" name="keyword1" />
<input type="text" name="keyword1" />
Then document.adv_search.keyword1.focus() will fail with the error you specify.
The reason is that:
document.adv_search.keyword1
is a shortcut for this syntax (which goes back to DOM Level 0 and the Netscape 2 days!):
document.forms.adv_search.elements.keyword1
(Incidentally, it is better to use this full syntax, instead of relying on the behaviour of the ‘document’ and ‘form’ objects being indexed on names: if a new method is added to HTMLDocument or HTMLFormElement, that might clash with the control name you are using. This is less of an issue when you use the document.forms or form.elements collections. Also, IE mistakenly dumps all names and ids into ‘document’, so if you've got an element with id="adv_search" in addition to the form with that as a name, document.adv_search will return the wrong one.)
Anyway, the DOM Level 0 scripting methods behave slightly curiously when you access an element by name like this. If there is a single matching element, you'll get that one as a standalone object. If, on the other hand, there are more than one, you'll get a list of objects. You can't call focus() or select() on an array-like list, which is why the error appears; you'd have to do something like keyword1[0].focus() when the list was returned.
So you have to decide whether you're going to be using old-school DOM Level 0 methods to access your form controls — in which case you're going to have to cope with sniffing for single-or-multiple-controls — or move to the ID-based methods introduced by ‘DOM Level 1’:
document.getElementById('keyword1').focus();
The ID-based methods are generally a bit more typing (in the script and to add ‘id’s to all elements you wish to access this way, if they don't already have them), but they are simple and unambiguous. (Also you can then drop the name on the <form> itself.)

The ID approach really is best but if you want to go by name, use getElementsByName.
In this case, it might look like this:
<script>
// retrieves array of objects with the name 'keyword1'
// and takes the first one
var key1 = document.getElementsByName('keyword1')[0];
key1.focus();
key1.select();
</script>

Related

javascript .value wont get anything [duplicate]

How can I get a collection of elements by specifying their id attribute? I want to get the name of all the tags which have the same id in the html.
I want to use ONLY getElementById() to get an array of elements. How can I do this?
I know this is an old question and that an HTML page with multiple identical IDs is invalid. However, I ran into this issues while needing to scrape and reformat someone else's API's HTML documentation that contained duplicate IDs (invalid HTML).
So for anyone else, here is the code I used to work around the issue using querySelectorAll:
var elms = document.querySelectorAll("[id='duplicateID']");
for(var i = 0; i < elms.length; i++)
elms[i].style.display='none'; // <-- whatever you need to do here.
The HTML spec requires the id attribute to be unique in a page:
[T]he id attribute value must be unique amongst all the IDs in the element's tree
If you have several elements with the same ID, your HTML is not valid.
So, document.getElementById should only ever return one element. You can't make it return multiple elements.
There are a couple of related functions that will return a list of elements: getElementsByName or getElementsByClassName that may be more suited to your requirements.
Why you would want to do this is beyond me, since id is supposed to be unique in a document. However, browsers tend to be quite lax on this, so if you really must use getElementById for this purpose, you can do it like this:
function whywouldyoudothis() {
var n = document.getElementById("non-unique-id");
var a = [];
var i;
while(n) {
a.push(n);
n.id = "a-different-id";
n = document.getElementById("non-unique-id");
}
for(i = 0;i < a.length; ++i) {
a[i].id = "non-unique-id";
}
return a;
}
However, this is silly, and I wouldn't trust this to work on all browsers forever. Although the HTML DOM spec defines id as readwrite, a validating browser will complain if faced with more than one element with the same id.
EDIT: Given a valid document, the same effect could be achieved thus:
function getElementsById(id) {
return [document.getElementById(id)];
}
document.querySelectorAll("#yourId"); returns all elements whose id is yourId
It is illegal to have multiple elements with the same id. The id is used as an individual identifier. For groups of elements, use class, and getElementsByClassName instead.
The id is supposed to be unique, use the attribute "name" and "getelementsbyname" instead, and you'll have your array.
As others have stated, you shouldn't have the same ID more than once in your HTML, however... elements with an ID are attached to the document object and to window on Internet Explorer. Refer to:
Do DOM tree elements with ids become global variables?
If more than one element with the same ID exists in your HTML, this property is attached as an array. I'm sorry, but I don't know where to look if this is the standard behavior or at least you get the same behavior between browsers, which I doubt.
Class is more than enough for refering anything you want, because it can have a naming with one of more words:
<input class="special use">
<input class="normal use">
<input class="no use">
<input class="special treatment">
<input class="normal treatment">
<input class="no special treatment">
<input class="use treatment">
that's the way you can apply different styles with css (and Bootstrap is the best example of it) and of course you may call
document.getElementsByClassName("special");
document.getElementsByClassName("use");
document.getElementsByClassName("treatment");
document.getElementsByClassName("no");
document.getElementsByClassName("normal");
and so on for any grouping you need.
Now, in the very last case you really want to group elements by id. You may use and refer to elements using a numerically similar, but not equal id:
<input id=1>
<input id="+1">
<input id="-1">
<input id="1 ">
<input id=" 1">
<input id="0x1">
<input id="1.">
<input id="1.0">
<input id="01.0">
<input id="001">
That way you can, knowing the numeric id, access and get an element by just adding extra non-invalidating numeric characters and calling a function to get (by parsing and so on) the original index from its legal string identifying value. It is useful for when you:
Have several rows with similar elements and want to handle its events
coherently. No matter if you delete one or almost all of them.
Since numeric reference is still present, you can then reuse them and
reassign its deleted format.
Run out of class, name and tagname identifiers.
Although you can use spaces and other common signs even when it's a not a requirement strictly validated in browsers, it's not recommended to use them, specially if you are going to send that data in other formats like JSON. You may even handle such things with PHP, but this is a bad practice tending to filthy programming practices.
This is my solution:
<script type="text/javascript">
$(document).ready(function () {
document.getElementsByName("mail")[0].value = "ex_mail1";
document.getElementsByName("mail")[1].value = "ex_mail2";
});
</script>
Or you can use for-loop for that.
You shouldn't do that and even if it's possible it's not reliable and prone to cause issues.
Reason being that an ID is unique on the page. i.e. you cannot have more than 1 element on the page with the same ID.
you can use
document.document.querySelectorAll("#divId")
we can use document.forms[0].Controlid
If you're using d3 for handling multiple objects with the same class / id
You can remove a subset of class elements by using d3.selectAll(".classname");
For example the donut graph here on http://medcorp.co.nz utilizes copies of an arc object with class name "arc" and there's a single line of d3, d3.selectAll(".arc").remove(); to remove all those objects;
using document.getElementById("arc").remove(); only removes a single element and would have to be called multiple times (as is with the suggestions above he creates a loop to remove the objects n times)

Functionality of Javascript functions and jquery selectors from within html

I have this javascript function:
function clearDiv(div_id) {
alert(div_id);
$(div_id).empty();
}
And the following html:
<input value="Clear" type="button" onClick="clearDiv(div_to_clear)" />
<div id="div_to_clear">
<!-- more html -->
</div>
Why is it that the above will actually find the javascript div object with id div_to_clear and use the $ selector to access it?
If I had done the input as :
<input value="Clear" type="button" onClick="clearDiv('div_to_clear')" />
I would need to change my function to
function clearDiv(div_id) {
alert(div_id);
$('#' + div_id).empty();
}
Is there any documentation about this? Are there advantages to using one method or the other?
IE (and Chrome in an effort for compatability) will create properties on the window with names of elements with ids, corresponding to those elements.
In the first example are are passing window.div_to_clear which points to your element directly. In the second, you are passing a string telling jQuery which element to select.
The first one is non-standard behavior so you should not rely on it.
The first one is actually a browser bug (they called it a feature) to access the DOM node by window.div_to_clear (the global variable) - and jQuery creates its wrapper around the element. For legacy reasons, it still exists in current browsers, but is deprecated. Your really should use the selector solution.
This is because there is a widely-implemented (although not best practice) method by browsers to automatically place html elements with id's into their correlating variable name. For example:
<div id="someId"></div>
will end up psuedo creating the variable someId which holds that html element.
These questions have similar information on the behavior:
Do DOM tree elements with ids become global variables?
Where does the variable holding an element with an id get stored?
Element accessible with ID
Here is a jsperformance test showing that accessing the id in that manner is slower than using document.getElementById: http://jsperf.com/global-id-vs-document-getelementbyid

Is there a way to find a descendant of a form with a particular name, without using [form element].[name attribute value]?

Consider this HTML:
<form id="MyForm">
<input name="Input1"/>
</form>
To get the form, I would do this:
var form = document.getElementById("MyForm");
Now I know that to get Input1 from the form I can do this:
var input1 = form.Input1;
Can you give me the code for another way to access any form control from a form, by using the name attribute?
I would imagine that a possible answer could involve recursing through descendants of the form and checking for a control with the attribute named "name", with the value "Input1".
Please provide an answer that does not require additional libraries.
The following is not important
In case you're wondering why I'm asking this: I'm using software called Script#, which compiles C# into JavaScript. The current version of Script# doesn't support [form element].[name attribute value], so I'm looking for an alternative way to do this.
You could give the document.getElementsByName function a shot.
An alternative you might be able to use is:
document.getElementById("MyForm")["Input1"]
Either that, or you need to assign an ID directly to the form element, and reference that. Otherwise, multiple forms may contain an element of the same name, and without including the form as part of the reference, you'd have an ambiguity.

javascript - name or id of element

Is this.form.sel2 similar to document.getElementById('sel2')?
My select tag is as follows:
<select size=5 id="sub_player_ids" name="sub[player_ids][]">
And when I am putting the name of the tag, i.e, sub[player_ids][] in my javascript code, am getting a syntax error.
I am trying to find a workaround so that instead of using the name of the element, i want to use the id.
However using document.getElementById('sub_player_ids') is not working.
Thanks for any suggestion provided.
Please see my javascript code below:
<input type="button" value="-->"
onclick="moveOptions(this.form.sel1, this.form.sel2);" /><br />
<input type="button" value="<--"
onclick="moveOptions(this.form.sel2, this.form.sel1);" />
The id of your element is sub_player_ids, not sel2. So document.getElementById("sub_player_ids") would work.
You may also find that this.form["sub[player_ids][]"] would work. Using the quoted form lets you use things that you can't use in the literal form.
Something to beware of is that IE7 and earlier have a broken version of getElementById that will find things that use the given string as a name, rather than as an id, even if something later on the page actually uses it as an id. (Yes, really; more here.) Some libraries will work around that for you (jQuery does, for instance). And actually, speaking of libraries, a good library really can help work around all sorts of browser inconsistencies and provide a lot of handy utility functionality, letting you concentrate on your actual business problems. You might consider looking at jQuery, Prototype, YUI, Closure, or any of several others.
You can use bracket notation instead:
this.form['sub[player_ids][]']
...or getElementById(), with the right ID:
document.getElementById('sub_player_ids')
Use document.getElementById('sub_player_ids') to get that element.
You have the wrong id
document.getElementById('sub_player_ids')
verify that your options contains id, it would only be containing name with sel2

is it normal for image inputs to be omitted from the DOM in document.forms[x].elements?

I've found that given a form in a HTML page like this:
<form name="form">
<input type="image" name="foo"
src="somewhere.gif" alt="image" value="blah"/>
<input type="text" name="bar" value="blah"/>
</form>
When accessing the elements via the DOM in Javascript, there is no element for the image input! It is just omitted. So, document.forms[0].elements.length is 1, and document.forms[0].element[0].type is "text".
This seems to be the case in Firefox, and IE. I can't find this fact documented anywhere in my reference books or on the web. All I can find is a throwaway comment here:
https://bugzilla.mozilla.org/show_bug.cgi?id=163822#c4
Which suggests it "just is like this". If so, well so be it - but is it really not documented anywhere? Is it a historical mistake, or is there a reason for it?
It looks like that's the behavior of the elements property in all browsers.
However, you should still be able to access it through the DOM in JavaScript using the childNodes property.
For your example:
document.forms[0].childNodes.length; // equals 5 (2 inputs and 3 text nodes).
document.forms[0].childNodes[1]; // This is your input with type='image'
Interesting... the DOM 1 spec defines .elements as:
elements
Returns a collection of all control elements in the form.
The HTML 4 spec part 17.2.1 doesn't list "image" types, so I guess that's the answer.
Indeed, I see a comment: "The DOM is supposed to work that way, that's how it works in Mozilla, NS4x, and IE. We can't change that even if we wanted to, lots of sites would break." so I would lean toward an historical error. Image element is already in HTML 2 DTD...
Perhaps that's for that and possible other culprits that authors discourage using Dom hierarchy like that in favor of getElement[s]ByXxx functions (or XPath!).
Been bitten by it myself. It's stated in the MSDN DHTML docs.

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