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localStorage array.push

Could someone tell me how to push elements into an array in localStorage?
My code:
(localStorage.getItem('projects') === null) ? localStorage.setItem('projects', ['proj1', 'proj2', 'proj3']) : '';
var ItemGet = localStorage.getItem('projects');
function CreateObject() {
console.log(ItemGet);
var Serializable = JSON.parse(ItemGet);
Serializable.push('proj4');
console.log(ItemGet);
}
<button onclick="CreateObject()">Add Object</button>

General approach:
let old_data = JSON.parse(localStorage.getItem('projects'))
let new_data = old_data.push(some_new_data)
localStorage.setItem('projects',JSON.stringify(new_data))

I would do the following assuming that your data is not a multiDimensional array.
(localStorage.getItem('projects') === null) ? localStorage.setItem('projects',
JSON.stringify(['proj1', 'proj2', 'proj3'])) : '';
var ItemGet = localStorage.getItem('projects');
function CreateObject() {
var Serializable = JSON.parse(ItemGet);
Serializable.push('proj4');
localStorage.setItem('projects',JSON.stringify(Serializable));
}

The problem you are hitting is that data stored in localStorage has to be a string. You'll have to parse/stringify before settting/getting anything from local storage. If you didn't want to work with strings, you may find something like IndexedDB API
const stuff = [ 1, 2, 3 ];
// Stringify it before setting it
localStorage.setItem('stuff', JSON.stringify(stuff));
// Parse it after getting it
JSON.parse(localStorage.getItem('stuff'));
Here is an example of using IndexedDB API from the docs
const dbName = "the_name";
var request = indexedDB.open(dbName, 2);
request.onerror = function(event) {
// Handle errors.
};
request.onupgradeneeded = function(event) {
var db = event.target.result;
// Create an objectStore to hold information about our customers. We're
// going to use "ssn" as our key path because it's guaranteed to be
// unique - or at least that's what I was told during the kickoff meeting.
var objectStore = db.createObjectStore("customers", { keyPath: "ssn" });
// Create an index to search customers by name. We may have duplicates
// so we can't use a unique index.
objectStore.createIndex("name", "name", { unique: false });
// Create an index to search customers by email. We want to ensure that
// no two customers have the same email, so use a unique index.
objectStore.createIndex("email", "email", { unique: true });
// Use transaction oncomplete to make sure the objectStore creation is
// finished before adding data into it.
objectStore.transaction.oncomplete = function(event) {
// Store values in the newly created objectStore.
var customerObjectStore = db.transaction("customers", "readwrite").objectStore("customers");
customerData.forEach(function(customer) {
customerObjectStore.add(customer);
});
};
};
There are also other solutions out there like PouchDB depending on your needs

Say for example you have an array. This is how you can store it in the local storage.
let my_array = [1, 2, 3, 4];
localStorage.setItem('local_val', JSON.stringify(my_array))
Now to push any data into the local storage array you have to override by the new data like bellow
let oldArray = JSON.parse(localStorage.getItem('local_val'))
oldArray.push(1000)
localStorage.setItem('local_val', JSON.stringify(oldArray))

Get specifics ids in IndexedDB [duplicate]

I want to execute this query
select * from properties where propertyCode IN ("field1", "field2", "field3")
How can I achieve this in IndexedDB
I tried this thing
getData : function (indexName, params, objectStoreName) {
var defer = $q.defer(),
db, transaction, index, cursorRequest, request, objectStore, resultSet, dataList = [];
request = indexedDB.open('test');
request.onsuccess = function (event) {
db = request.result;
transaction = db.transaction(objectStoreName);
objectStore = transaction.objectStore(objectStoreName);
index = objectStore.index(indexName);
cursorRequest = index.openCursor(IDBKeyRange.only(params));
cursorRequest.onsuccess = function () {
resultSet = cursorRequest.result;
if(resultSet){
dataList.push(resultSet.value);
resultSet.continue();
}
else{
console.log(dataList);
defer.resolve(dataList);
}
};
cursorRequest.onerror = function (event) {
console.log('Error while opening cursor');
}
}
request.onerror = function (event) {
console.log('Not able to get access to DB in executeQuery');
}
return defer.promise;
But didn't worked. I tried google but couldn't find exact answer.

If you consider that IN is essentially equivalent to field1 == propertyCode OR field2 == propertyCode, then you could say that IN is just another way of using OR.
IndexedDB cannot do OR (unions) from a single request.
Generally, your only recourse is to do separate requests, then merge them in memory. Generally, this will not have great performance. If you are dealing with a lot of objects, you might want to consider giving up altogether on this approach and thinking of how to avoid such an approach.
Another approach is to iterate over all objects in memory, and then filter those that don't meet your conditions. Again, terrible performance.
Here is a gimmicky hack that might give you decent performance, but it requires some extra work and a tiny bit of storage overhead:
Store an extra field in your objects. For example, plan to use a property named hasPropertyCodeX.
Whenever any of the 3 properties are true (has the right code), set the field (as in, just make it a property of the object, its value is irrelevant).
When none of the 3 properties are true, delete the property from the object.
Whenever the object is modified, update the derived property (set or unset it as appropriate).
Create an index on this derived property in indexedDB.
Open a cursor over the index. Only objects with a property present will appear in the cursor results.
Example for 3rd approach
var request = indexedDB.open(...);
request.onupgradeneeded = upgrade;
function upgrade(event) {
var db = event.target.result;
var store = db.createObjectStore('store', ...);
// Create another index for the special property
var index = store.createIndex('hasPropCodeX', 'hasPropCodeX');
}
function putThing(db, thing) {
// Before storing the thing, secretly update the hasPropCodeX value
// which is derived from the thing's other properties
if(thing.field1 === 'propCode' || thing.field2 === 'propCode' ||
thing.field3 === 'propCode') {
thing.hasPropCodeX = 1;
} else {
delete thing.hasPropCodeX;
}
var tx = db.transaction('store', 'readwrite');
var store = tx.objectStore('store');
store.put(thing);
}
function getThingsWherePropCodeXInAnyof3Fields(db, callback) {
var things = [];
var tx = db.transaction('store');
var store = tx.objectStore('store');
var index = store.index('hasPropCodeX');
var request = index.openCursor();
request.onsuccess = function(event) {
var cursor = event.target.result;
if(cursor) {
var thing = cursor.value;
things.push(thing);
cursor.continue();
} else {
callback(things);
}
};
request.onerror = function(event) {
console.error(event.target.error);
callback(things);
};
}
// Now that you have an api, here is some example calling code
// Not bothering to promisify it
function getData() {
var request = indexedDB.open(...);
request.onsuccess = function(event) {
var db = event.target.result;
getThingsWherePropCodeXInAnyof3Fields(db, function(things) {
console.log('Got %s things', things.length);
for(let thing of things) {
console.log('Thing', thing);
}
});
};
}

How to properly use Parse / Promise?

I am writing some JavaScript codes using Parse.com.
To be honest, I have been reading how to use Promise and done lots of research but cannot still figure out how to use it properly..
Here is a scenario:
I have two tables (objects) called Client and InvoiceHeader
Client can have multiple InvoiceHeaders.
InvoiceHeader has a column called "Amount" and I want a total amount of each client's InvoiceHeaders.
For example, if Client A has two InvoiceHeaders with amount 30 and 20 and Client B has got nothing, the result I want to see in tempArray is '50, 0'.
However, with the following codes, it looks like it's random. I mean sometimes the tempArray got '50, 50' or "50, 0". I suspect it is due to the wrong usage of Promise.
Please help me. I have been looking into the codes and stuck for a few days.
$(document).ready(function() {
var client = Parse.Object.extend("Client");
var query = new Parse.Query(client);
var tempArray = [];
query.find().then(function(objects) {
return objects;
}).then(function (objects) {
var promises = [];
var totalForHeader = 0;
objects.forEach(function(object) {
totalForHeader = 0;
var invoiceHeader = Parse.Object.extend('InvoiceHeader');
var queryForInvoiceHeader = new Parse.Query(invoiceHeader);
queryForInvoiceHeader.equalTo('headerClient', object);
var prom = queryForInvoiceHeader.find().then(function(headers) {
headers.forEach(function(header) {
totalForHeader += totalForHeader +
parseFloat(header.get('headerOutstandingAmount'));
});
tempArray.push(totalForHeader);
});
promises.push(prom);
});
return Parse.Promise.when.apply(Parse.Promise, promises);
}).then(function () {
// after all of above jobs are done, do something here...
});
} );

Assuming Parse.com's Promise class follows the A+ spec, and I understood which bits you wanted to end up where, this ought to work:
$(document).ready(function() {
var clientClass = Parse.Object.extend("Client");
var clientQuery = new Parse.Query(clientClass);
clientQuery.find().then(function(clients) {
var totalPromises = [];
clients.forEach(function(client) {
var invoiceHeaderClass = Parse.Object.extend('InvoiceHeader');
var invoiceHeaderQuery = new Parse.Query(invoiceHeaderClass);
invoiceHeaderQuery.equalTo('headerClient', client);
var totalPromise = invoiceHeaderQuery.find().then(function(invoiceHeaders) {
var totalForHeader = 0;
invoiceHeaders.forEach(function(invoiceHeader) {
totalForHeader += parseFloat(invoiceHeader.get('headerOutstandingAmount'));
});
return totalForHeader;
});
totalPromises.push(totalPromise);
});
return Parse.Promise.when(totalPromises);
}).then(function(totals) {
// here you can use the `totals` array.
});
});

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.

Efficient way to broadcast from sockjs-node?

I'd like to broadcast messages to all clients connected to my sockjs-node server.
Right now I have the following code
var clients = {};
var echo = sockjs.createServer();
echo.on('connection', function(conn) {
clients[conn.id] = conn;
for(key in clients) {
if(clients.hasOwnProperty(key)) {
clients[key].write('test');
}
}
conn.on('close', function() {
delete clients[conn.id];
});
});
Is there a more efficient way to do it ?
Maybe
var clients = [];
var echo = sockjs.createServer();
echo.on('connection', function(conn) {
var index = clients.push(conn);
var lenght = clients.length;
while(length--) {
if(clients[length] !== undefined) {
clients[length].write('test');
}
}
conn.on('close', function() {
delete clients[index];
});
});
Thanks

1.)for...in is slower then regular for or while, not by much
2.)also probably getting a value from an object is slower then getting a value from an array (cause you need to get address from a string, but you can calculate address from an array index imminently), also not by much
So second one is faster.