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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);
}
});
};
}

Javascript Object Issue not able to send particular key

Hi i have a weird javascript issue.Here's my code I am not able to send these keys in my designOrder object. My Object does not have these fronImage and backImage keys that i am sending in my code.
let designOrder = await dbCall();
let allImages = []
allImageIds.push(designOrders.frontImageId);
allImageIds.push(designOrders.backImageId);
allImages = await dbCall();
let allImagesHash = {};
allImages.forEach(obj) => {
obj.image = JSON.parse(image)
allImagesHash[image.id] = image;
}
if(designOrder.backImageId){
designOrder.backImage = allImagesHash[designOrder.backImageId]
}
// if i do console.log("1", designOrder.backImage) it will log the designOrder.backImage
if(designOrder.frontImageId){
designOrder.frontImage = allImagesHash[designOrder.frontImageId]
}
// if i do console.log("2", designOrder.frontImage) it will log the designOrder.backImage
// but while console.log("3", designOrder) it will not show the backImage and frontImage keys
return designOrder;

It actually solved it after the first dbCall() i have added this line of code and it worked.
designOrder = designOrder.toJSON();
toJson function is defined within the mongoose schema.

How to add item to local storage

I am creating a song book app with 'add to favorite' button. i have song1.html song2.html and favorite.html.
in song1.html, when add to favorite button is clicked. i am storing the link to that song in local storage.
This is my song1.html
<!DOCTYPE html>
<html>
<body>
<button onclick="mySongOne()">add to favorite</button>
<script>
function mySongOne() {
localStorage.setItem("favsong", "<a href='https://www.song1.com'><h1>song1</h1></a>");
}
</script>
</body>
</html>
in song2.html, when add to favorite button is clicked. i am storing the link of the second song in local storage.
song2.html
<!DOCTYPE html>
<html>
<body>
<button onclick="mySongTwo()">add to favorite</button>
<script>
function mySongTwo() {
localStorage.setItem("favsong", "<a href='https://song2.com'><h1>song2</h1></a>");
}
</script>
</body>
</html>
now i have a favorite.html for listing my favourite songs. and favourite.html will retrieve the links that i stored in local storage.
favorite.html
<!DOCTYPE html>
<html>
<body onload="myFunction()">
<div id="result"></div>
<script>
function myFunction() {
document.getElementById("result").innerHTML = localStorage.getItem("favsong");
}
</script>
</body>
</html>
Now i want to show both song 1 and song 2 in favorite.html.
but only song 2 is displayed in favourite.html. How to accomplish this.

Store list in javascript Array.
You need to either use different keys or store multiple strings in array and then JSON.stringify that to save in localStorage.
Similary when you get the same string from localStorage then convert it into object using JSON.parse.
<!DOCTYPE html>
<html>
<body>
<div id="result"></div>
<script>
// Check browser support
if (typeof(Storage) !== "undefined") {
// Store
let list = [];
list.push("<h1>John<h1>");
list.push("<h2>David<h2>");
localStorage.setItem("list", JSON.stringify(list));
// Retrieve
document.getElementById("result").innerHTML = JSON.parse(localStorage.getItem("list"));
} else {
document.getElementById("result").innerHTML = "Sorry, your browser does not support Web Storage...";
}
</script>
</body>
</html>

When using localStorage, you can only have one item per key. localStorage allows you to store string-data as the value, thus we can use JSON.
You can serialize an array of items you want to add and then append them to the key inside of localStorage.
References:
JSON.stringify()
JSON.parse()
localStorage
JSFiddle. StackOverflow doesn't allow localStorage so I hosted my code there.
Code:
let items = ['<h1>John<h1>', '<h2>David<h2>', '<h3>Mary<h3>', '<h4>Bob<h4>'];
// Stringify the array and store it
localStorage.setItem("list", JSON.stringify(items));
// Parse the stringified array back from localStorage
let itemsRetrieved = JSON.parse(localStorage.getItem('list'));
// Get div with .list class
let div = document.querySelector('.list');
// Iterate retrieved array and append items
itemsRetrieved.forEach(item => {
div.innerHTML += item;
});
// Add an item
itemsRetrieved.push('<span style="color: red;">Dylan</span>');
// Stringify the new array and overwrite the key
localStorage.setItem("list", JSON.stringify(itemsRetrieved));
Code [For those who love encapsulation]:
let items = ['<h1>John<h1>', '<h2>David<h2>', '<h3>Mary<h3>', '<h4>Bob<h4>'];
// Stringify the array and store it [Initial]
localStorage.setItem("list", JSON.stringify(items));
// Returns parsed array
function getData(key) {
return JSON.parse(localStorage.getItem(key));
}
// Returns new array
function addData(key, item) {
// Get current array
let currentData = getData(key);
// Add an item
currentData.push(item);
// Stringify the new array and overwrite the key
localStorage.setItem(key, JSON.stringify(currentData));
return currentData;
}
// Parse the stringified array back from localStorage
let itemsRetrieved = getData('list');
// Get div with .list class
let div = document.querySelector('.list');
// Add an item
itemsRetrieved = addData('list', '<span style="color: red;">Dylan</span>');
// Iterate retrieved array and append items
itemsRetrieved.forEach(item => {
div.innerHTML += item;
});

If you really need to append data to the same LocalStorage key, there is no built-in append function.
However, you can use a custom function, for instance the one proposed in this answer: https://stackoverflow.com/a/7680123/2446264, and get the following code to do what you want:
<!DOCTYPE html>
<html>
<body>
<div id="result"></div>
<script>
// Check browser support
if (typeof(Storage) !== "undefined") {
// Store
localStorage.setItem("list", "<h1>John<h1>");
appendToStorage("list", "<h2>David<h2>");
// Retrieve
document.getElementById("result").innerHTML = localStorage.getItem("list");
} else {
document.getElementById("result").innerHTML = "Sorry, your browser does not support Web Storage...";
}
function appendToStorage(name, data){
var old = localStorage.getItem(name);
if(old === null) old = "";
localStorage.setItem(name, old + data);
}
</script>
</body>
</html>

Basically, you'll need to store those data as a list of strings (or use different keys 'list1', 'list2' etc...).
So, when you are putting your value into the local storage initially, you'll need to do something like this:
var initialValue = ['<h1>John<h1>']; // array of strings
// since Local Storage accepts only string values,
// you can store an array or any other object by using JSON.stringify function
localStorage.setItem('list', JSON.stringify(initialValue);
// updating local storage
var list = JSON.parse(localStorage.getItem('list');
list.push('<h2>David<h2>');
localStorage.setItem('list', JSON.stringify(list));
Then you can append those value by looping through the list.
var output = '';
for (var i = 0; i < list.length; i++) {
output = output + list[i];
}
document.getElementById("result").innerHTML = output;

What you are doing wrong:
localstorage doesn't store data types, but rather stores a string.
For instance, if you was to store an integer in a localstorage property, the data type would always be returned as a string.
Since you are attempting to store an array of values, you will need to create a CSV (comma-separated values) method.
var strLocalStorage = "John, Peter, Fred, Paul, Mary, Elizabeth";
You can the parse this into local storage using one of two methods
JSON (See example beneath)
SPLIT (variable.split(", ");
It is important you should be aware, Browsers set limitations of 5MB of data allocated between LocalStorage and SessionStorage.
This can cause problems when a large amount of data needs to be stored, in the event of your edited example, storing various URLs
What may be an alternative to your solution, would be to create CSV of favourite songs using your SQL Table's unique ID for the song table entry.
However, in the event your code is only using Front End languages such as HTML and JAVASCRIPT, then you may prefer to use IndexedDB
How to use Indexed DBs
This will allow you to create a local database that is accessible offline and allows you to recall and edit the values easier such as
LocalStorage Example:
var blLocalStorage = false;
function funInitiate(){
if (typeof(Storage) !== "undefined") {
console.log("localstorage detected on this browser");
blLocalStorage = true;
}else{
console.log("local storage is not supported by this browser, please update");
}
}
function funTestLocalStorage(){
var strLocalStorage = localStorage.getItem("FavSongs");
if(strLocalStorage === null){
return false;
}else{
return true;
}
}
function funGetSongFavorites(){
if(blLocalStorage){
if (funTestLocalStorage()){
var arrLocalStorage = JSON.parse(localStorage.getItem("FavSongs"));
var elOutput = document.querySelector("#result");
for(i = 0; i < arrLocalStorage.length; i++){
elOutput.innerHTML += "<br>" + arrLocalStorage[i]
}
}
}else{
console.log("No local storage - function funGetSongFavourites aborted");
}
}
function funAddFav(strURL){
if(blLocalStorage){
var strLocalStorage = localStorage.getItem(strURL);
if(strLocalStorage === null){
localStorage.setItem("FavSongs", strURL);
}else{
var arrList = JSON.parse(localStorage.getItem('FavSongs'));
arrList.push(strURL);
}
localStorage.setItem('FavSong', JSON.stringify(arrList));
console.log("Favourite Lists update: " + strURL);
}else{
console.log("No local storage - Function funAddFav aborted");
}
}
document.addEventListener("DOMContentLoaded", funInitiate, false);
<!DOCTYPE html>
<html>
<head>
<title>Webpage Title</title>
<script src="pathToJSScriptShownBeneath"></script>
</head>
<body>
<button onclick="funAddFav('http://youtube.com')">
Add to favorite
</button>
<div id="result"></div>
</body>
</html>
Indexed DB example
var songList = [
{ id: 1, artist: "2pac", title: "Dear Mama", URL: "https://www.youtube.com/watch?v=Mb1ZvUDvLDY" },
{ id: 2, artist: "Biggie Smalls", title: "Hypnotize", URL: "https://www.youtube.com/watch?v=glEiPXAYE-U" }
];
const dbName = "favSongs";
var request = indexedDB.open(dbName, songList.length);
request.onerror = function(event) {
console.log("An Error has occured, script will now exist";
return;
};
request.onupgradeneeded = function(event) {
var db = event.target.result;
var objectStore = db.createObjectStore("SongList", { keyPath: "id" });
// There can be multiple songs by 1 artist or band therefore this will
// declare this as a false unique entry, the sample applies for song titles
// some songs have the same title but performed by different artists.
objectStore.createIndex("artist", "artist", { unique: false });
objectStore.createIndex("title", "title", { unique: false });
// Song URLs will be unique, so we set this as a individually unique
objectStore.createIndex("URL", "URL", { 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("favSongs", "readwrite").objectStore("SongList");
customerData.forEach(function(songList) {
customerObjectStore.add(songList);
});
};
};
// Retrieving Data:
var transaction = db.transaction(["favSongs"]);
var objectStore = transaction.objectStore("SongList");
var request = objectStore.get(2);
request.onerror = function(event) {
console.log("Entry doesnt exist of has been deleted");
};
request.onsuccess = function(event) {
var strArtist = request.result.artist;
var strTitle = request.result.title;
var strURL = request.result.URL;
};
// Deleting Data
var request = db.transaction(["favSongs"], "readwrite")
.objectStore("SongList")
.delete(1);
request.onsuccess = function(event) {
console.log ("Entry 1 has been deleted");
};

Add item: localStorage.name = 'Name'
Get item: let name = localStorage.name
Remove item: localStorage.removeItem('name')

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;
}
});