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How to use Javascript to check whether a value of a column in a Sharepoint list is either empty or null?

So far I can retrieve the list based on a string I pass and even the column names but I can't figure out how to get the values of a specific column. Here is what I have so far.
function GetFieldList()
{
var listname = document.getElementById("ListName").value;
var ctx = SP.ClientContext.get_current();
this.web = ctx.get_web();
ctx.load(this.web);
this.list = web.get_lists().getByTitle(listname);
ctx.load(this.list);
this.fields = this.list.get_fields();
ctx.load(this.fields);
ctx.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}
Btw I'm using SharePoint 2010.

I think your code is not full the client Context must run async method to load the values
If you want correct way to get the values from SharePoint read the this documentation :
https://msdn.microsoft.com/en-us/library/office/hh185007(v=office.14).aspx
or you can use another library such as rest api or spservice .
Anyway the get_fields() return the fields list name not values.

As you said SP.ClientContext.get_current(); is an Javascript Object, so first of all you need to check if the property that you want to know if is null or empty, exists.
var ctx = SP.ClientContext.get_current();
isPropertyEmptyOrNull = ctx.hasOwnProperty('myProperty') && (prop.myProperty === null or prop.myProperty === '' or prop.myProperty === undefined)
You found more details abour hasOwnProperty here

Refer below code. This shows how to retrieve items from SharePoint list.
function GetItems() {
var context = new SP.ClientContext.get_current();
var list = context.get_web().get_lists().getByTitle('ListName');
var camlQuery = new SP.CamlQuery();
camlQuery.set_viewXml("");
collItems = list.getItems(camlQuery);
context.load(collItems);
context.executeQueryAsync(GetItemsSuccess, GetItemsFail);
}
function GetItemsSuccess() {
var listItemEnumerator = collItems.getEnumerator();
if (collItems.get_count() > 0) {
while (listItemEnumerator.moveNext()) {
var oListItem = listItemEnumerator.get_current();
/*
retrieve specific fields (e.g. Title, FirstName...)
Here 'Title' and 'FirstName' will be the internal name of the field you want to retrieve
*/
var title = oListItem.get_item('Title');
var firstName = oListItem.get_item('FirstName');
}
}
}
function GetItemsFail(sender, args) {
// Error handler code
}

Sharepoint 2013 Javascript - Get List Fields

I am on a double learning curve with SharePoint 2013 development and JavaScript.
Please refer to below.
function GetListFields(listname, viewname, ResultCallBackFunction)
{
var clientContext = new SP.ClientContext.get_current();
var web = clientContext.get_web();
var list = web.get_lists().getByTitle(listname);
if (viewname == "")
{
var view = list.get_views().getByTitle(viewname);
var listFields = view.get_viewFields();
}
else
{
this.listFields = list.get_fields().getByInternalNameOrTitle("Title");
}
clientContext.load(this.listFields);
clientContext.executeQueryAsync(onListFieldsQuerySucceeded, onListFieldsQueryFailed);
function onListFieldsQuerySucceeded()
{
console.log(listFields.get_fields().getByInternalNameOrTitle("Title").get_internalName());
var fldArray = new Array();
var fieldEnumerator = listFields.getEnumerator();
while (fieldEnumerator.moveNext())
{
var oField = fieldEnumerator.get_current();
fldArray.push(oField);
}
ResultCallBackFunction(fldArray);
}
function onListFieldsQueryFailed()
{
alert("Something went wrong. The End is Nigh.");
}
}
The intent is to call GetListFields to return an array with the list's fieldnames. This returns an error "Unable to get property 'get_fields' of undefined or null reference" at the line "console.log....". Please note that this is for my debugging.
If I change the code for function GetListFields as follows:
var clientContext = new SP.ClientContext.get_current();
var web = clientContext.get_web();
var list = web.get_lists().getByTitle(listname);
if (viewname == "")
viewname = "All Items";
var view = list.get_views().getByTitle(viewname);
this.listFields = view.get_viewFields();
I DO get a result but this contains a field named 'LinkTitle' which I do not have in my list because I have renamed this. What am I missing?
Further to the above, I got an error when using
var listFields = ...
which fixed by doing
this.listFields = ...
but do not understand the difference.
Thanks for any help or pointers.

I took a moment to test your code in my Sharepoint 2013 environment.
I made some changes and now it works.
You can see the resulting script bellow.
Here is some important information about the field names in the result array.
The names of the fields in the view returned by Sharepoint are the internal names and not the title of the field.
This is the reason why you get LinkTitle instead of the real title of your field.
When you create a field in the Sharepoint interface, Sharepoint create a title for the field and also an internal name based on the title.
For example, if I create a field named « my test field », Sharepoint will say the title of the field is « my test field » and the internal name is « my_x0020_test_x0020_field ».
<script>
function GetListFields(listname, viewname, ResultCallBackFunction)
{
var clientContext = new SP.ClientContext.get_current();
var web = clientContext.get_web();
var list = web.get_lists().getByTitle(listname);
var listFields;
var view;
var defaultViewName = 'All Items';
if (viewname === "")
{
viewname = defaultViewName;
}
view = list.get_views().getByTitle(viewname);
listFields = view.get_viewFields();
clientContext.load(listFields);
clientContext.executeQueryAsync(onListFieldsQuerySucceeded, onListFieldsQueryFailed);
function onListFieldsQuerySucceeded()
{
var fldArray = new Array();
var fieldEnumerator = listFields.getEnumerator();
while (fieldEnumerator.moveNext())
{
var oField = fieldEnumerator.get_current();
fldArray.push(oField);
}
ResultCallBackFunction(fldArray);
}
function onListFieldsQueryFailed()
{
alert("Something went wrong. The End is Nigh.");
}
}
function MyCallBack(fieldArray) {
for (var x=0;x<fieldArray.length;x++) {
console.log(fieldArray[x]);
}
}
</script>
<a id="callGetListFields" href="#" onclick="GetListFields('MyListName','MyViewName', MyCallBack);">Call function GetListFields</a>
Hope this help!

Saving data in localstorage

I'm try to save data to localstorage. Created "class" through constructor and try to put get and set methods to them. But when I click my button(when button was clicked data must be saving) nothing happens(In developer tools "Resource" tab). When I tried simple save data through JSON.stringify and else all was worked.
(function() {
window.onload = function() {
document.getElementById('buttonCreate').onclick = function() {
var topicValue = document.getElementById("create-topic").value;
var statusValue = document.getElementById("create-status").value;
var descriptionValue = document.getElementById("create-description").value;
var storage = new Storage();
var ticket = {
topic: topicValue,
status: statusValue,
description: descriptionValue
};
storage.set("Item", item);
}
}
})();
"class" Storage:
function Storage() {
this._ITEMS_DESCRIPTOR = 'items';
}
Storage.prototype.get = function() {
var fromStorage = localStorage.getItem(this._ITEMS_DESCRIPTOR);
return fromStorage ? JSON.parse(fromStorage) : [];
};
Storage.prototype.set = function(key, items) {
localStorage.setItem(key, JSON.stringify(items));
};

The exact issue with your code is the storage key and also the item that you are trying to store which is not defined.
It stores it in to Item key and the get method is written to take it from the key, items.
by looking at the given code, you should suppose to store ticket object. storage.set(ticket);
A suggested better approach: To pass a key to instantiate Storage object and then use it accordingly.
Such as var storage = new Storage('Item');
(function() {
window.onload = function() {
document.getElementById('buttonCreate').onclick = function() {
var topicValue = document.getElementById("create-topic").value;
var statusValue = document.getElementById("create-status").value;
var descriptionValue = document.getElementById("create-description").value;
var storage = new Storage("ticket");
var ticket = {
topic: topicValue,
status: statusValue,
description: descriptionValue
};
storage.set(ticket);
}
}
})();
"class" Storage:
function Storage(key) {
this._ITEMS_DESCRIPTOR = key;
}
Storage.prototype.get = function() {
var fromStorage = localStorage.getItem(this._ITEMS_DESCRIPTOR);
return fromStorage ? JSON.parse(fromStorage) : {};
};
Storage.prototype.set = function(item) {
localStorage.setItem(this._ITEMS_DESCRIPTOR, JSON.stringify(item));
};
To get the ticket value stored in localstorage:
var storage = new Storage('ticket');
var ticket = storage.get();

Per Mike McCaughan's comment, you were referencing an undefined variable.
Using strict mode would have caught this.
You have another bug in the keys used to address items in storage:
'items' !== 'Item'
Also; you have no classes in your code.

How to concatenate values from a pop-up window choice with values from a database?

I am developing a project with the Kendo UI Framework, using more specically the Scheduler widget and I have the current issue:
On my database I have two tables one called Events and the other one called TypeOfEvents. Each type of event has got a specific color, a specific title plus defined values for startHour and endHour fields.
When the pop-up window to create an event is called, I can choose on two kendoMultiSelect the correspondent user and the type of event.
I can also choose the startDate and endDate. The default behavior of a Scheduler widget has got two datetimepickers also, however, I don't want that option on my pop-up window because the events will have defined hours that an user can't change.
My idea would be the following one:
Once I click save after choosing a specific event on my MultiSelectList, there would be some way to concatenate the startHour and endHour values I have defined in my database with the startDate and endHour field that I choosed on the pop-up window.
Right now, all my events startDate/endDate fields are saved on my DB with this format: 2015-03-01 00:00:00.000
I would like to substitute all those zeros with the values I defined in advance in my startHour/endHour fields of my TypeOfEvents table.
Here's my current CREATE script:
create: function (createEvent) {
var typeOfEventID = $("#selectEvent").val();
var usernameID = $("#selectUsername").val();
var dataStartTemp = $("#dataStart").val();
var dataEndTemp = $("#dataEnd").val();
var note = $("#note").val();
var res = $("#customViewScheduler").data("kendoScheduler");
var res1 = res.resources[1].dataSource.data();
var dataStart = convertToJSONDate(dataStartTemp);
var dataEnd = convertToJSONDate(dataEndTemp);
var changeSet = [];
var id = 0;
usernameID.forEach(function (userID) {
typeOfEventID.forEach(function (eventID) {
var titletemp = $.grep(res1, function (elem) {
if (elem.TypeOfEventID == eventID) {
return true;
}
})
if (titletemp.length > 0) {
note = titletemp[0].title;
}
var entityChange = {};
entityChange.Id = id;
entityChange.Entity = {
'__type': "Events:#BlahBlahWeb",
'UsernameID': userID,
'TypeOfEventID': eventID,
'startDate': dataStart,
'endDate': dataEnd,
'Title': note
};
entityChange.Operation = 2;
changeSet.push(entityChange);
id++
})
})
var changesetPayload = JSON.stringify({
"changeSet": changeSet
});
//Create jQuery ajax request
var Params = {}
Params.type = "POST";
Params.url = "./../Services/BlahBlahWeb-BlahDomainService.svc/JSON/SubmitChanges";
Params.dataType = "json";
Params.data = changesetPayload;
Params.contentType = "application/json";
Params.error = function (httpRequest, textStatus, errorThrown) {
//SendErrorByEmail(errorThrown, httpRequest.responseText)
}
Params.success = function (data) {
//createEvent.success(data);
var scheduler = $("#customViewScheduler").data("kendoScheduler");
var elem = tratanewelem(data.SubmitChangesResult[0].Entity)
scheduler.dataSource.read();
}
//Make the ajax request
$.ajax(Params);
},
Any idea of how can I accomplish that?

knockout push values array

when I click on button1 I get object with 50 contacts array (containing collection of arrays with phoneNumbers, Addresses...), then when I click on button 2 I get the same object but my first object is erased whereas I would like to display 50 + 50 = 100 contacts array. I tried concat method but I have some difficulties to implement.
viewModel.initializeListener = function() {
$('#button1').click(function() {
document.getElementById("button2").style.visibility = "hidden";
$('#retrievedContactsDiv').html('');
nbDisplayedContacts = 0;
console.info("test");
viewModel.ui.FlashbackReport.MoreContacts();
});
$('#button2').click(function() {
viewModel.ui.FlashbackReport.MoreContacts();
console.info("test");
});
}; `
viewModel.WeHaveMoreContacts = function(data) {
console.info("test:", data)
if (viewModel.MoreContacts) {
var newArray=ko.mapping.fromJS(data, viewModel.MoreContacts);
var concatenated = newArray.concat(dataArray);
viewModel.MoreContacts.contacts(concatenated);
} else {
viewModel.MoreContacts = ko.mapping.fromJS(data);
var dataArray = viewModel.MoreContacts.contacts();
}
I have a parameter with number of contacts to skip for the server.
function which call the server then call the mapping function :
viewModel.ui.FlashbackReport.MoreContacts()
Problem : Object # has no method 'concat'

I made a fiddle that may help you.
The first part of the function generates new contacts and the second one add them to the existing contacts.
var VM = function () {
var self = this;
self.contacts = ko.observableArray();
self.addMore = function () {
// simulate server response
var offset = self.contacts().length;
var dataFromServer = [];
for (var index = 0; index < 10; index++) {
dataFromServer.push({
name: 'contact ' + offset + index
});
}
// add each new item to existing items.
ko.utils.arrayForEach(dataFromServer, function (item) {
self.contacts.push(item);
});
};
}
Feel free to ask more explanation.
I hope it helps.