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What is a faster way to write this function to delete rows/objects in a table?

So, I have this function that, after an update, deletes elements from a table. The function, lets call it foo(), takes in one parameter.
foo(obj);
This object obj, has a subfield within called messages of type Array. So, it would appear something like this:
obj.messages = [...];
Additionally, inside of obj.messages, each element contains an object that has another subfield called id. So, this looks something like:
obj.messages = [{to:"You",from:"Me",id:"QWERTY12345.v1"}, ...];
Now, in addition to the parameter, I have a live table that is also being referenced by the function foo. It uses a dataTable element that I called oTable. I then grab the rows of oTable and copy them into an Array called theCurrentTable.
var theCurrentTable = oTable.$('tr').slice(0);
Now, where it gets tricky, is when I look into the Array theCurrentTable, I returned values appear like this.
theCurrentTable = ["tr#messagesTable-item-QWERTY12345_v1", ...];
The loop below shows how I tried to show the problem. While it works (seemingly), the function itself can have over 1000 messages, and this is an extremely costly function. All it is doing is checking to see if the current displayed table has the elements given in the parameter, and if not a particular element, delete it. How can I better write this function?
var theCurrentTable = oTable.$('tr').slice(0);
var theReceivedMessages = obj.messages.slice(0);
for(var idx = 0; idx < theCurrentTable.length; idx++){ // through display
var displayID = theCurrentTable[idx].id.replace('messagesTable-item-','').replace('_','.');
var deletionPending = true;
for(var x = 0; x < theReceivedMessages.length; x++){
var messageID = theReceivedMessages[x].id;
if(diplayID == messageID){
console.log(displayID+' is safe...');
deletionPending = false;
}
}
if(deletionPending){
oTable.fnDeleteRow(idx);
}
}

I think I understand your problem. Your <tr> elements have an id that should match an item id within your messages.
First you should extract the message id values you need from the obj parameter
var ids = obj.messages.map(function (m) { return '#messagesTable-item-' + m.id; });
This will give you all the rows ids you need to keep and then join the array together to use jQuery to select the rows you don't want and remove them.
$('tr').not(ids.join(',')).remove();
Note: The Array.prototype.map() function is only supported from IE9 so you may need to use jQuery.map().

You could create a Set of the message ID values you have, so you can later detect if a given ID is in this Set in constant time.
Here is how that would look:
var theCurrentTable = oTable.$('tr').slice(0);
var theReceivedMessages = obj.messages.slice(0);
// Pre-processing: create a set of message id values:
var ids = new Set(theReceivedMessages.map( msg => msg.id ));
theCurrentTable.forEach(function (row, idx) { // through display
var displayID = row.id.replace('messagesTable-item-','').replace('_','.');
// Now you can skip the inner loop and just test whether the Set has the ID:
if(!ids.has(displayId)) {
oTable.fnDeleteRow(idx);
}
});
So now the time complexity is not any more O(n.m) -- where n is number of messages, and m the number of table rows -- but O(n+m), which for large values of n and m can make quite a difference.
Notes:
If theCurrentTable is not a true Array, then you might need to use a for loop like you did, or else use Array.from(theCurrentTable, function ...)
Secondly, the implementation of oTable.fnDeleteRow might be that you need to delete the last rows first, so that idx still points to the original row number. In that case you should reverse the loop, starting from the end.

How to get selected values of Kendo Multi Select?

I'm using Kendo multi select as follow but i can't get selected values
var multiselect = $("#SelectRoles").data("kendoMultiSelect");
var selectedData= [];
var items = multiselect.value();
for (var itm in items)
{
selectedData.push(itm);
}
but array selectedData return indices of items in multiselect not values .

You can also assign the array, returned from the value() method, directly to the variable, e.g.:
var ms = $("#multiselect").kendoMultiSelect({
value: ["1", "2"]
}).data('kendoMultiSelect');
var selectedItems = ms.value();
console.log(selectedItems); // ["1", "2"]

Use this other one returns indices.
var multiselect = $("#SelectRoles").data("kendoMultiSelect");
var selectedData= [];
var items = multiselect.value();
for (var i=0;i<items.length;i++)
{
selectedData.push(items[i]);
}

Your original code doesn't look wrong. Are you sure you are getting only indices? Perhaps you should post your MultiSelect code as well. I found this question because I had the same problem and used the other answers for reference, but I found them overcomplicated. So let me answer in another complicated way :)
Here's what I've got. I know it's more code than you need, but I think it's important to see the full picture here. First let me set this up. There's a problem with the Kendo().MultiSelect.Name("SomeName") property if you are using it more than once. "Name" sets not only the html name, but the id as well, and you never want two ids with the same identifier. So in my code, I am appending a unique Id to my MultiSelect.Name property to ensure a unique id. I am putting the MultiSelect in each row of a table of people. I am showing this to make sure you are using the DataValueField property so you are able to get the selected values (not the text you see in the ui). If you are just showing a list of text values with no id behind them, perhaps that is why you are getting the wrong data?
#foreach (var cm in Model.CaseMembers)
{
<tr>
<td>
#(Html.Kendo().MultiSelect()
.Name("IsDelegateFor" + cm.CaseMemberId)
.Placeholder("is a delegate for..")
.DataTextField("FullName")
.DataValueField("CaseMemberId")
.BindTo(Model.Attorneys)
)
</td>
</tr>
}
then, later on, in my jQuery where I attempt to extract out the DataValueField (CaseMemberId), which is the array of selected values of the MultiSelect...
var sRows = [];
$('#cmGrid tr').each(function () {
// 'this' is a tr
$tr = $(this);
// create an object that will hold my array of selected values (and other stuff)
var rec = {};
rec.IsADelegateFor = [];
// loop over all tds in current row
$('td', $tr).each(function (colIndex, col) {
if (colIndex === 3) {
// make sure our MultiSelect exists in this td
if ($(this).find("#IsDelegateFor" + rec.CaseMemberId).length) {
// it exists, so grab the array of selected ids and assign to our record array
rec.IsADelegateFor = $(this).find("#IsDelegateFor" + rec.CaseMemberId).data("kendoMultiSelect").value();
}
}
}
// add this tr to the collection
sRows.push(rec);
}
so this is all a super verbose way of saying that this single line, as the other people mentioned works perfectly to grab the ids. There is no need to iterate over the .value() array and push the contents to another array!
rec.IsADelegateFor = $(this).find("#IsDelegateFor" + rec.CaseMemberId).data("kendoMultiSelect").value();
So in your original code, there is no reason the following should not work,
var multiselect = $("#SelectRoles").data("kendoMultiSelect");
var selectedData = [];
selectedData = multiselect.value();
console.log(selectedData);
unless
you don't have your MultiSelect set up properly in C# with DataValueField
you have multiple MultiSelects on the page with the exact same id and it's reading from a different one than you think.
You don't even have value fields, just a list of text.

var selected = $("#multi").data("kendoMultiSelect").value();

The solution given by volvox works.
Below is jquery version,
var multiselect = $("#SelectRoles").data("kendoMultiSelect");
var selectedData= [];
var items = multiselect.value();
$.each(items ,function(i,v){
selectedData.push(v);
});

How to work with variables dynamically in javascript?

I need to work with variables dynamically, and get them dynamically too. The first thing I need to know is:
How to save a variable reference(NOT its value) in a collection?
Example:
var divA = "<div>my div A</div>";
var divB = "<div>my div B</div>";
var divC = "<div>my div C</div>";
Then, save in a collection:
var mySet = new Set();
function returnDivA(){
return divA;
}
function returnDivB(){
return divB;
}
function returnDivC(){
return divC;
}
mySet.add(returnDivA());//I would like save the varible ref in a collection.
mySet.add(returnDivB());
mySet.add(returnDivC());
I want the Set collection to save the variables(NOT its values), it means:
var mySet = new Set(divA, divB, divC);
Then, with that, my intent is to do something like that:
var totalOfDivs;
for(var i = 0; i < mySet.size; i++){
totalOfDivs += mySet[i];
}
$("#anotherDIV_to_show_all_divs").html(totalOfDivs);//Then, here, I want to show all divs in the screen.
I would like suggestions, please!

It solved my problem to put variable dynamically in html using this in a for loop:
$("#anotherDIV_to_show_all_divs").append(mySet[i]);
About saving javascript variable reference in a Collection, I understand that I can't do that, because of the answer of the adeneo in comment:
"There is no "reference", all variables are pass-by-value in javascript..."

Read the documentation about set.
enter link description here
I guess you have to loop your set like this.
var totalOfDivs= "";
for (let item of mySet.values()) {
totalOfDivs+= item;
//console.log(item);
}
$("#anotherDIV_to_show_all_divs").html(totalOfDivs);

How to create array with variables?

I have an svg map with several points where I want to store the initial position of each point in an array. And each point has it's own ID, like point_1, point_2 etc.
I have attached a click handler to each of these and run a function when they are clicked.
So what I want to do in this function is to check if the array already contains the information of the clicked element. If it doesn't, I want to create it.
This is what I want to do, in pseudo code
var arrPoints = [];
zoomToPoint('point_1');
function zoomToPoint(data_id) {
// Does array already contain the data?
if (!arrPoints.data_id) {
// Add data to the array
arrPoints.data_id.clientX = somevalue;
arrPoints.data_id.clientY = somevalue;
}
}
This would basically create an array that looks like this:
arrPoints.point_1[]
arrPoints.point_2[]
Where I can access the data in each .point_1 and .point_2.
But I can't create an array based on a variable, like this:
arrPoints.data_id = [];
Because I end up with data_id as the actual name, not the variable that data_id actually is. So how is this usually accomplished? How can I identify each point to the actual array?
Sorry for my lack of basics

Just use an object:
var arrPoints = {};
zoomToPoint('point_1');
function zoomToPoint(data_id) {
// Does array already contain the data?
if (!arrPoints[data_id]) { // square brackets to use `data_id` as index
// Add data to the array
arrPoints[data_id] = {};
arrPoints[data_id].clientX = somevalue;
arrPoints[data_id].clientY = somevalue;
}
}

Global var in JavaScript

This is annoying me.
I'm setting an array in beginning of the doc:
var idPartner;
var myar = new Array();
myar[0] = "http://example.com/"+idPartner;
And I'm getting a number over the address, which is the id of partner. Great. But I'm trying to set it without success:
$.address.change(function(event) {
idPartner = 3;
alert(idPartner);
}
Ok. The alert is giving me the right number, but isn't setting it.
What's wrong?

Changing the value of the variable does not re-set the values within the array. That is just something javascript can't do automatically. You would have to re-generate the array for it to have the new id. Could you add the id to the value where you use the array instead of pre-setting the values in the array containing the id?
Edit: For example, you would do:
var myArray = [];
var myId = 0;
myArray[0] = "http://foo.com/id/";
and when you need to use a value from the array, you would do this:
var theVal = myArray[0] + myId;

Try this:
var myvar = ["http://site.com/"];
$.address.change(function(event) {
myvar[1] = 3;
}
then use myvar.join () where you need the full url.

The problem here is that at the line
myar[0] = "http://site.com/"+idPartner;
..you perform a string concatenation, meaning you copy the resulting string into the array at index position 0.
Hence, when later setting idPartnerit won't have any effect on the previously copied string. To avoid such effect you can either always construct the string again when the idPartnervariable updates or you create an object and you evaluate it when you need it like...
var MyObject = function(){
this.idPartner = 0; //default value
};
MyObject.prototype.getUrl = function(){
return "http://site.com/" + this.idPartner;
};
In this way you could use it like
var myGlblUrlObj = new MyObject();
$.address.change(function(event){
myGlblUrlObj.idPartner = ... /setting it here
});
at some later point you can then always get the correct url using
myGlblUrlObj.getUrl();
Now obviously it depends on the complexity of your situation. Maybe the suggested array solution might work as well, although I prefer having it encapsulated somewhere in an object for better reusability.

myar[0] = "http://site.com/" + idPartner;
After this line, myar[0] = "http://site.com/undefined" and it has nothing to do with the variable idPartner no more.
So, after that changing the value of idPartner will affect the value of myar[0].
You need to change the value of myar[0] itself.