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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))

JavaScript Class Objects not returning value

I've been working with the Microsoft Bot Framework to create a bot that can interface between MS Teams and AWS. I've been trying to write some JS functions but have been unsuccessful in getting them to operate how I want them to.
Here is what I am currently working on and am stuck on:
I am creating a 'ping' like functionality so a bot user can ping an instance in AWS and receive its status whether its running and has passed the system checks or not. My code is currently able to take the user request for the ping, retrieve the information from AWS, and can even print that info to the console. However, when I am trying to retrieve that information back out of the object that I set it to and print it to MS Teams, it says my variable is undefined.
Some code snippets are below:
class aws_Link {
constructor (mT, ping_1, i_state, i_status) {
this.myTag = mT;
this.ping = ping_1;
this.instance_state = i_state; // I declare this here, but should I?
this.instance_status = i_status; // I declare this here, but should I?
}
//i_state and i_status are just passed NULL when the object is initialized
//so they would be holding some value, not sure if I have to do this
api_link () {
var mainLink = API_LINK_TAKEN_OUT_FOR_OBVIOUS_REASONS;
var myTagFill = "myTag=";
var ampersand = "&";
var pingFill = "ping=";
var completeLink = String(mainLink + myTagFill + this.myTag + ampersand + pingFill + this.ping);
var finalLink = completeLink;
finalLink = finalLink.split(' ').join('');
//set up API-key authenticication
var options = {
url: finalLink,
headers: {
'x-api-key': 'AWS-PRIVATE-TOKEN'
}
};
if(this.ping == "TRUE") { // if the user wants to use /ping
var res = request(options, function(error, response, body) {
console.log("PING REQUEST"); //debug
body = JSON.parse(body);
var h_state = body['instanceState'];
var h_status = body['instanceStatus'];
this.instance_state = h_state;
this.instance_status = h_status;
console.log("STATE: " + h_state); //debug
console.log("STATUS: " + h_status); //debug
});
}
}
pingFunction () {
var tmp = "Instance State: " + this.instance_state + " Instance Status: " + this.instance_status;
return tmp;
}
}
And here is where I call the api_link() function and pingFunction():
var apiLink1 = new aws_Link("MY_TAG_VALUE", "TRUE", "NULL", "NULL");
var completeAPILink = apiLink1.api_link();
session.send('Request complete.');
session.send("PING: " + apiLink1.pingFunction());
So essentially the user enters in some info which gets passed to where I create the "new aws_Link" which then a my understanding is, creates an object called apiLink1. From there, it makes the request to AWS in my api_link() function, which retrieves the info I want. I thought I was then saving this info when I do the: this.instance_state = h_state; & this.instance_status = h_status;. So then when I call pingFunction() again on apiLink1, I thought I would be able to retrieve the information back out using this.instance_state and this.instance_status, but all it prints out is undefined. Any clarification on why my current code isn't working and any changes or improvements I can make would be greatly appreciated.
Thanks!

Get an unknown key name from Firebase function database trigger

I'm new to Firebase functions and trying to understand how to get a certain key from the database .onCreate trigger. Here is an example:
exports.createUserRoundData =
functions.database.ref('/data/players/{user_key}/').onCreate(event => {
var eventData = event.data.val();
var userKey = event.params.user_key;
var itemKey = eventData.items; // This returns an object
});
The structure is:
players > user_key > items > item_key > data
In the above scenario how can I retrieve the item_key?

Yes you can,
You need something like this :
exports.createUserRoundData = functions.database.ref('/data/players/{user_key}/').onCreate(event => {
var userKey = event.params.user_key; // Get user key parameter
var eventSnapshot = event.data; // Get player data
var itemsSnapshot = eventSnapshot.child('items'); // Get items data
itemsSnapshot.forEach(function(itemSnapshot) { // For each item
var itemKey = itemSnapshot.key; // Get item key
var itemData = itemSnapshot.val(); // Get item data
});
});
Here the Firebase Cloud Functions documentation.

Node/Javascript only send changed values

I'm writing a simple application where I send values to a mqtt broker given by a pot-meter (variable resistor). The thing I am trying to accomplish is that I only send changed values to save bandwidth. I am trying Object.observe, but that does not do anything. Can anybody help me?
My code:
var analogValue = 0;
every((0.5).second(), function() {
analogValue = my.sensor.analogRead();
var values = {values:[{key:'resistance', value: analogValue}]}
//another experiment here
var arr = ['resitance', analogValue];
Array.observe(arr, function(changes) {
console.log(changes);
});
arr[1] = analogValue
console.log('sent ',values,'to ',thingTopic)
client.publish(thingTopic, JSON.stringify(values));
});
var o = [analogValue];
Object.observe(o, function (changes) {
console.log(changes);
//eventually publish only changes to broker here
})
o.name = [analogValue]

You don't need to use Object.observe. You can just save the last measurement and check the new one against it. Like this:
// I'm assuming that any actual measurement will be different than 0
var lastMeasurement = 0;
every((0.5).second(), function() {
var analogValue = my.sensor.analogRead();
if (lastMeasurement !== analogValue) {
// the new value is different
var values = {values:[{key:'resistance', value: analogValue}]};
client.publish(thingTopic, JSON.stringify(values));
// update the last measurement value
lastMeasurement = analogValue;
}
});

Storing arrays in localStorage error

I have a bug in my code that only saves the last object in an array upon reload. I have a feeling that my addAccount() function is not saving or inserting data correctly. Everything else works correctly. In my console, it shows that the data is being inserted into the array, but when I refresh I only get the last object saved.
I'm not sure what to do.
// The list of accounts array.
var accountsArray = [];
function addAccount() {
// Take fields and put user data into varables.
var accountName = document.getElementById('accountName').value;
var accountBalance = document.getElementById('accountBalance').value;
var accountType = document.getElementById("accountType");
var accountTypeSelected = accountType.options[accountType.selectedIndex].text;
var accountCurrency = document.getElementById("accountCurrency");
var accountCurrencySelected = accountCurrency.options[accountCurrency.selectedIndex].text;
var temporaryObject = {
'accountName': accountName,
'accountBalance': accountBalance,
'accountTypeSelected': accountTypeSelected,
'accountCurrencySelected': accountCurrencySelected
};
accountsArray.push(temporaryObject);
console.log(accountsArray);
saveAccountData();
showAccountsArray();
}
function saveAccountData() {
localStorage.setItem('accountsArray', JSON.stringify(accountsArray));
}
function showAccountsArray() {
//var accountsLocalStorage = JSON.parse(localStorage['accountsArray']);
if (localStorage.getItem("accountsArray") === null) {
document.getElementById("getStarted").style.visibility="visible";
document.getElementById("balanceToolbarName").style.visibility="hidden";
document.getElementById("accountsMainList").style.visibility="hidden";
} else {
var accountsLocalStorage = JSON.parse(localStorage['accountsArray']);
console.log(accountsLocalStorage);
var accountInfo = '';
var i = 0;
while (i < accountsLocalStorage.length) {
accountInfo += '<li class="swipeout"><div class="swipeout-content item-content"><div class="item-inner"><div class="item-title">' + accountsLocalStorage[i].accountName + '</div><div class="item-after">$' + accountsLocalStorage[i].accountBalance + '</div></div></div><div class="swipeout-actions-left"><a href="#" class="action1">Clear</div><div class="swipeout-actions-right">Delete</div></a></li>';
document.getElementById("accountsList").innerHTML = accountInfo;
i++;
}
document.getElementById("getStarted").style.visibility="hidden";
document.getElementById("balanceToolbarName").style.visibility="visible";
document.getElementById("accountsMainList").style.visibility="visible";
}
}
*

all of your functions work correctly as tested by the link you've provided. When the page loads it successfully retrieves the data (if any) from the local storage and displays on the page. However, the global array variable accountsArray is populated with data retrieved from the local storage.
You need to repopulate the global array otherwise when you call saveAccountData it will save whatever the array holds which indeed overrides whatever you had in the local storage. To fix it, simply add add this code block...
$(function(){
var data = localStorage.getItem("accountsArray");
if(data != null)
accountsArray = JSON.parse(localStorage.getItem("accountsArray"));
});