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Access multiple elements with ID from within a node, but also with specific class

I need to retrieve all elements who's ID ends with "_inputError" from within a specific element! AND also , I need to retrieve only the inputError that has class 'b-block' set.. How would I do this using javascript/jquery ?
I know I can get my form node with: var formNode = $("#frm1");
I know I can get ALL elements with ID ending, but this will get them all, which isn't quite what I need: var inputErrors = $("[id$=_inputError]");.
How do I mix'em all together as to retrieve only the input errors with 'd-block' class from within a specified form node ?
Cheers!
UPDATE: This seems to work for me:
var inputErrors = $("[id$=_inputError].d-block");
console.warn(inputErrors[0]);
It'll retrieve all inputError with class .d-block. However, I've yet to find how to do this check ONLY from a selected form element id, instead of the hole page. (I can have multiple forms on a single page!)

To help others if it can, here's the final solution and why I needed this:
Essentially, I get a response back from an ajax post like so:
{
type: 2,
formid: 'frmProfile',
fields: {
username: "Invalid username!",
email: "Invalid email!"
}
}
I loop my response.fields to show the individual errors under each failed inputs.
I then needed to find a way set focus on the first failed input! Because my fields are NOT 0-indexed based, I could not simply set the focus on the first field in the array! They are 'randomly' looped through!
Therefor, I decided to get all input errors that we're showing (id=*_inputError and with class d-block). The first one in the returned array is in fact the first input error! So, I use its ID to determine the corresponding input name and set focus to it:
var inputErrors = $("#" + response.formid + " [id$=_inputError].d-block");
var firstInputError = inputErrors[0].id.replace(/_inputError$/, ''); // get just the name of the failed input! Its name/id should be the same as <name>_inputError!
document.getElementById(firstInputError).focus();
This seems to do the trick for me ;) Hopefully, this can serve ideas to others.
Thanks for your help folks!
P

problem with use of val() in jQuery sometimes failing and setting elements with array id's

I have a project where a form is required for inputs for a week, so for efficiency elsewhere an array of inputs is used (i.e. start[0] etc) this seems to have exacerbated the issue.
The problem is when validating a form where some inputs are given initial values (its an update) jQuery only returns those initial values instead of changed ones unless use of 'this' is feasible. I found to resolve that I had to use:
$(".weekdays").change(function(){
var newval = $(this).attr('value');
$(this).attr('value', newval);
});
Which seems a crazy thing to have to do! Its here I found using $(this).val(newval); always fails except when setting initial values, though its the common given solution?
In the same vein setting check-boxes seems also problematical, using:
var id = $(this).attr('pid');
$("#choice["+id+"]").prop('checked', false);
$("#choiceLabel["+id+"]").css('background-image','url("images/Open.png")');
Always fails, yet reverting to javascript with:
var id = $(this).attr('pid');
document.getElementById("choice["+id+"]").checked = false;
document.getElementById("choiceLabel["+id+"]").style.backgroundImage = 'url("images/Open.png")';
Works fine!
So does jQuery not like inputs with id's in array form? or am I getting things wrong somewhere?

When attempting to select an element with an id that contains special characters, such as [], you have to remember to escape them for jQuery. For instance..
var id = 12;
console.log(
$('#choice\\['+ id +'\\]').get()
);
console.log(
$('#choice[data-something]').get()
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="choice[12]">weee</div>
<div id="choice" data-something>dang!</div>
Otherwise, jQuery will treat them as special characters, in this case, assuming you are trying to find an element that has an id and has an attribute matching your variable value.

determining if a field exists on a form

I have a form field (a series of checkboxes) that's being created dynamically from a database, so it's possible that the field will not exist on the form (if there are no matching values in the database). I have some code that needs to execute based on whether the field exists, and pull in the values that are selected if it does exist. I can't seem to get javascript to acknowledge that this field exists, though. Here's what I've tried:
function displayAction(){
var f = document.adminForm;
var a = f.action;
if(f.prefix.value!="-") {
a = a + '&task=callExclusionDisplay&prefix=' + f.prefix.value;
}
else {
var exclusions = document.getElementById("exclusions");
if (exclusions != null){
alert("exclusions set");
a = a + '&task=callExclusionCreate&prefix=' + f.prefix.value + '&exclusions=' + exclusions.join();
}
}
alert('after if, action is ' + a);
}
The code never passes the if statement checking to see if exclusions is not null, even though when I look at the page there are a number of checkboxes named exclusions (with the id also set to exclusions). Is the issue with !=null because it's a group of checkboxes, rather than a single form element? How can I get this to work? If I skip the test for null, the code throws errors about exclusions not being defined if the database doesn't return any matching values.

You're using document.getElementById, but form elements have a name.
Try f.elements.namedItem("exclusions") instead of exclusions != null

Multiple elements in the same page cannot share an id attribute (ie. id must be unique or unset). As well, though some (older) browsers erroneously collect elements whose name matches the ID being looked for with getElementById, this is invalid and will not work cross-browser.
If you want to get a group of elements, you can give them all the same name attribute, and use document.getElementsByName to get the group. Note that the result of that will be a NodeList which is kind of like an array in that it can be iterated over.

Do all the checkboxes have the same id == exclusions?
If yes, then you must first correct that.
Before you do so, did you try checking the first checkbox and see if the if condition goes through?

if you have more than one element with the id "exclusions" it will screw up the functionality of getElementById. I would remove the duplicate "exclusions" ids from all of your elements and use getElementByName() instead, and give your group of checkboxes the name="exclusions" instead.
Edit:
But there is a much simpler way using jQuery, and it gives you some cross browser compability guarrantee. To do the same thing with jQuery do this:
var checkBoxesExist = $('[name=exclusions]').count() > 0;
Or if you have given your elements unique ID's then you can do this:
var checkbox1exists = $('#checkBox1').count() > 0;

Each element must have a unique ID.
Then, you can check just like this:
if (document.getElementById('exclusions1')) {
//field exists
}
Or if you need to loop through a bunch of them:
for (x=0; x<10; x++) {
if (document.getElementById('exclusions' + x)) {
//field X exists
}
}

How to avoid javascript retrieving values from non-existing elements

Update: clarified question (I hope)
Hi.
I'm developing a plugin in Wordpress and I'm outputting elements according to user privileges A and B.
In case of A, I ouput element "Foo".
In case of B, I output element "Bar".
Up till now, I haven't checked if an element exists before I try to retrieve the value.
This of course gives me a javascript error in some browsers (like IE7).
I've looked at using the typeof() function:
if(typeof(element) == 'undefined') {
//do something...
}
I'm also using jQuery. So one solution could be using this:
if ($("#mydiv").length > 0){
// do something here
}
Using the above methods, makes me having to check each element before trying to retrieve any values.
The "ideal" solution would be to get values based on user privileges. E.g:
if (userPriv == A) {
//get values from element 'Foo'
}
This way I can check once, and do the data gathering. The only solutions I can think of are setting the value of a hidden input element or use cookies.
<input type="hidden" id="userPriv" value="A" />
The other solution would be adding a value to the cookie.
setcookie("userPriv", "A");
Unfortunately, this last option gives me a warning message saying that cookie must be set in header (before html output). I think it's because I'm doing this in Wordpress.
I'm looking for opinions on which method is "the best way" to accomplis this.

Forgive me if I'm missing something, but checking for a DOM element in javascript is usually pretty easy.
var elementA = document.getElementById('id_of_a');
var elementB = document.getElementById('id_of_b');
if (elementA) {
//...
} else if (elementB) {
//...
}
The key is the if statement. getElementById will return nothing null if the element is not found, which will evaluate to false in the if statement.
Alternatively, if you don't really want to check for existence of individual DOM elements, can you send the users priv in a hidden input and act on that? That's a cookie free way of sending values clientside. Something like (edited to have jQuery code instead)
<input type="hidden" id="userPriv" value="A" />
...
var priv = $('#userPriv').val();
if (priv == 'A') {
//...
}
I'd still recommend checking for individual elements over checking a hidden input. It seems cleaner to me, more along the unobtrusive lines

You can use object as associative array:
var map = new Object();
map[A.toString()] = new Foo();
map[B.toString()] = new Bar();
In that case is much simpler to check and you will avoid "spaghetti code".

Locating text and performing operation based on its existence

I'm trying to learn jQuery, but it's coming slowly as I really don't know any JavaScript.
My site is in VB.NET and I'm putting jQuery code on both my actual .ascx UserControl and in a separate file (something like myscripts.js). This is because I'm using webforms as I still don't know MVC well enough to implement it, so I have to get the clientID's on the page.
What I would like to do is the following:
Grab text from a textbox and make it all lowercase
Get the username from the login info. I've done this like so on my actual page:
var userName = "<%=Split(System.Web.HttpContext.Current.User.Identity.Name.ToLowerInvariant, '|')%>";
Check to see if the username is in the text. If it IS in the text, I want to set a variable to "false", othewise to true.
How do I do this?

I am completely ignorant of the ASP.NET side of it, but as far as jQuery and Javascript....
To get the value of a text field, you use the jQuery function val():
var value = $('#mytextbox').val();
To turn a string to lower case, you use the string method toLowerCase():
var value = $('#mytextbox').val().toLowerCase();
Since val() returns a string we can throw that at the end.
To check if a string is within another string, you use the string method indexOf():
var needle = 'Hello';
var haystack = 'Hello World';
var match = haystack.indexOf(needle); // -1 if no matches, 0 in this case

Another thing to remember is that ASP.NET renames all your control ID's. To access your controls in JavaScript, you should use the following in place of the Control ID <%= txtUserName.ClientID %>.
In jQuery, here is what my selector would look like for a textbox with the ID "txtUserName".
$('#<%= txtUserName.ClientID %>')
Enjoy,
Zach

var userName = "username as it comes out of your web app";
// stuff happens
var $myTextbox = $('#ID_of_textbox');
var userNameIsContained = $myTextbox.val().toLowerCase().indexOf(userName) >= 0;
Short explanation:
$('#ID_of_textbox') // fetches the jQuery object corresponding to your textbox
.val() // the jQuery function that gets the textbox value
.toLowerCase() // self explanatory
.indexOf() // returns the position of a string in a string (or -1)
See the JavaScript String object reference at w3schools.
Alternative (to check if the textbox value equals the username):
var userNameIsEqual = $myTextbox.val().toLowerCase() == userName;

The basics of JQuery are like so: Find a list of dom elements, and perform actions on them.
In your case, you should start off by finding the dom element that is your testbox. For example's sake, we'll choose $('#userName'). The selector # means "id" and together with the name "userName" it finds all elements with the id of "userName". (Ids on a page should be unique if you're following best practices.)
Once you have that list (in this case, a list of one element), you can ask it what the value is.
$('#userName').val()
This gets you the value of the value="" attribute of the input tag.
You can then assign it to a variable and use standard javascript String functions to do the rest!

function checkLogin(userName){
return $('#mytextbox').val().toLowerCase() == userName
}

if ($("#textBoxID").val()) != "") { /*Do stuff*/ }