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How Can I set variable width with !importanat using JavaScript/jQuery

Ia have a div named "#idDayNrCell". I want to get its width then do some calculations and apply it to another div called ".event". I am using bootstrap so i need to apply !important aswell. I am new to javascript/jquery.
I tried something like this. But it didn't wotk
$(document).ready(function(){
var cellWDTstr = ($("#idDayNrCell").css("width")); //get width
var cellWDT = cellWDTstr.substr(0,cellWDTstr.length-2); //remove the "px" part
console.log(cellWDT);
var GunSayisi=2; //how long is the event (2 for example)
// after tihs things get complicated for me
// if the even is minimum 2 days i need a different width. calculated below
var wdtEnAz2 = ((cellWDT-30)*GunSayisi + 30*(GunSayisi-1)).toString();
console.log(wdtEnAz2);
var setWdt = GunSayisi>1 ? wdtEnAz2 : calWdt;
//after here it is expoerimental code which I am failed
console.log(setWdt);
setWdt+= 'px';
console.log(setWdt);
$(".event").style.setPsetProperty('width',setWdt,'important');
});
this is the html

Using ES6,
var width = "100px";
$(".event").attr('style', `width: ${width} !important`);

Add like this :
$('.event').attr('style', 'width: '+ setWdt +' !important');

You can use css property from jquery, please find below code snippet :
$(".event").css( "width", function(
setWtd ) {
return setWtd + '!Important';
});

Create tag element dynamically and apply styles

I have created "myCanvas" div element dynamically and try to set styles to the div tag it throw the undefined exception. Please check my code and suggest me
// move the canvas, so it's contained by the same parent as the image
var imgParent = img.parentNode;
$('<div id="myCanvas">');
var can = $('myCanvas');
can.appendTo(imgParent);
// position it over the image
can.style.left = x + 'px'; //If set styles to can element, it's styles is undefined
What i did wrong here.. ? please anyone suggest me a right things..
Thanks,
Bharathi

Make is simple:
$('<div id="myCanvas">').appendTo(img.parentNode).css('left', x);

You don't need to select the myCanvas element because it hasn't been added to the DOM just yet (your selector wasn't right either). You can use this instead:
var imgParent = img.parentNode;
// By default when creating an element in jQuery, it returns an instance of the jQuery object created
var can = $('<div id="myCanvas">');
can.appendTo(imgParent);
can.style.left = x + 'px';

Replace
var can = $('myCanvas');
with
var can = $('#myCanvas');
[edit user="dholakiyaankit"]
QA asking for id not class

Antegias response should read
Replace ... with :
var can = $('#myCanvas');
as you have given it an id not a class, you cant select it in this way till its added to DOM, but you have a reference to it anyway in the variable can

setAttribute not working

I am making a plugin for form validation as practice, but for some reason after I create a h2 element and try to set it's attribute, it is not working. Here is the code
var testing = function(regex, value, error_msg, error_msg_field_id){
var pattern = new RegExp(regex);
if (!pattern.test(value)){
var ele = document.createElement("H2");
var node = document.createTextNode(error_msg);
ele.setAttribute('style', 'color:white');
alert("hi");
jQuery(error_msg_field_id).append(node);
}
}
the text appears with no problem, but it is not in white color. This make no sense at all to me

You are using setAttribute correctly, but you are setting the property on your h2-element, which is never actually inserted in your DOM.
You can change and simplify the relevant section of your code to:
var ele = document.createElement("H2");
ele.textContent = error_msg;
ele.setAttribute('style', 'color:white');
jQuery(error_msg_field_id).append(ele);
The usage of jQuery here is also not necessary. You can simply use
document.querySelector("#" + error_msg_field_id).appendChild(ele);
which is equally simple.

Remove Style on Element

I was wondering if this is possible.
There's this element
<div id="sample_id" style="width:100px; height:100px; color:red;">
So I want to remove width:100px; and height:100px;
the result would be
<div id="sample_id" style="color:red;">
Any help would be apprreciated. :)

You can edit style with pure Javascript. No library needed, supported by all browsers except IE where you need to set to '' instead of null (see comments).
var element = document.getElementById('sample_id');
element.style.width = null;
element.style.height = null;
For more information, you can refer to HTMLElement.style documentation on MDN.

var element = document.getElementById('sample_id');
element.style.removeProperty("width");
element.style.removeProperty("height");

Use javascript
But it depends on what you are trying to do. If you just want to change the height and width, I suggest this:
{
document.getElementById('sample_id').style.height = '150px';
document.getElementById('sample_id').style.width = '150px';
}
TO totally remove it, remove the style, and then re-set the color:
getElementById('sample_id').removeAttribute("style");
document.getElementById('sample_id').style.color = 'red';
Of course, no the only question that remains is on which event you want this to happen.

Update: For a better approach, please refer to Blackus's answer in the same thread.
If you are not averse to using JavaScript and Regex, you can use the below solution to find all width and height properties in the style attribute and replace them with nothing.
//Get the value of style attribute based on element's Id
var originalStyle = document.getElementById('sample_id').getAttribute('style');
var regex = new RegExp(/(width:|height:).+?(;[\s]?|$)/g);
//Replace matches with null
var modStyle = originalStyle.replace(regex, "");
//Set the modified style value to element using it's Id
document.getElementById('sample_id').setAttribute('style', modStyle);

$("#sample_id").css({ 'width' : '', 'height' : '' });

You can simply set that style to [unset], It forces CSS to pretend that style was never assigned to the given element.
var element = document.getElementById('sample_id');
element.style.width = "unset";
element.style.height = "unset";

Specifying auto on width and height elements is the same as removing them, technically. Using vanilla Javascript:
images[i].style.height = "auto";
images[i].style.width = "auto";

Just use like this
$("#sample_id").css("width", "");
$("#sample_id").css("height", "");

Access a label's attribute using jquery

I have some data coming from the server in which I fill A Div in the Html page with.
The way I write the div is as follows:
<div class="BigDiv"><label class = "AttList" Std_Id="' + Std_Id + '">' + Std_Name +'</label></div>
Now, I want the data inside this div.
There are some other labels inside the div so I use this.children to access this label.
var labels = $(this).children('div');
var StdName = this.children[0].childNodes[0].nodeValue;
I want to access the Std_Id inside the Std_Id attribute, but I don't know how to do it ... Do you have any ideas?
Thanks.

Assuming that $(this) is a reference to the .BigDiv element:
var StdName = $(this).find('label').attr('Std_Id');
Or, similarly, and with the assumption that this is the .BigDiv element:
var children = this.childNodes;
for (var i=0,len=children.length; i<len; i++){
if (children[i].nodeType == 1 && children[i].tagName.toLowerCase() == 'label'){
var StdName = this.getAttribute('Std_Id');
}
}
References:
jQuery:
attr().
find().
JavaScript
element.getAttribute().
node.nodeType.
tagName.
toLowerCase().

Use getAttribute:
var labels = $(this).children('div');
var StdId = this.children[0].getAttribute("Std_Id");
Note that, according to the HTML5 spec, custom attributes should start with data-, though most browsers can tolerate it.

To save elements, which were selected using a jQuery-Selector, do this:
$labels = $('.BigDiv').find('label');
Now you can loop through each label with jQuery's foreach loop:
$.each($labels, function() {
var std_id = $(this).attr('Std_Id');
// do something with std_id
});

You could use the attr method as such,
var value = $('.AttList').attr('Std_Id');
EDIT
OK, so you for your implementation, you need to do this...
var value = $(this).find('.AttList').attr('Std_Id');
Assuming that this is the div or the parent of that div