I am converting a table that was previously working but locking the UI during some tasks to be managed by a web worker. One of the functions I am updating is sorting. My old Sort function has been converted to:
function mySort(column){
myWorker.postMessage({ message: "sort", column: column.id });
}
In my worker:
self.onmessage = function (e) {
switch (e.data.message) {
case "sort":
DoSort(e.data.column);
break;
}
}
var m_sortCol;
function DoSort(column) {
if (m_sortCol != null && column.equals(m_sortCol)) // <---- The problem is here
myData.reverse();
else {
m_sortCol = column;
myData.sort(column);
}
}
The problem is, when my worker gets to the indicated line, it throws an exception, column.equals is not a function. Looking at the data in the Debugger, both column and m_sortCol have values, and they sure look like strings, though I don't see anywhere the object type is explicitly stated. I have tried changing the statement to column.toString().equals(m_sortCol.toString()), and the exception changes to column.toString(...).equals is not a function.
This code previously worked before changing to a web worker. Could the web worker be messing with my types somehow so that what looks like a string isn't actually a string? Or could the worker not have access to String functions somehow? My research says web workers should have String functions, but I am at a loss for how to explain this.
I suspect your string prototype has been modified, since there is no .equals function on the standard Javascript string type. In this case, you should simply be using == or ===. (This is an example of why modification of the string prototype is considered bad form in Javascript).
I have this network visualized using d3 and angular. Here is the link to the visualization.
I wanted to save the last state of the network so that even if I refresh the page it will show the last state. But don't know how to do that.
I read that it can be done using sessionStorage or localStorage but I can't seem to figure it out for my visualization.
I tried this by setting my JSON data to the sessionStorage and then getting it:
if (sessionStorage) {
sessionStorage.setItem("myKey", myJSON.toString());
}
if (sessionStorage) {
sessionStorage.getItem("myKey"); // {"myKey": "some value"}
}
and I also tried it like this:
localStorage.setItem("networkGraph", networkGraph);
var networkGraph = localStorage.getItem("networkGraph");
but it's not working. Is this the right way to do it?
Any help will be highly appreciated!
Are you sure that you need sessionStorage and not localStorage? In the case of sessionStorage saved data will be deleted when a browser tab with your app becomes closed.
You can write localStorage.setItem('inputLayerHeight', vm.inputLayerHeight); in your onChange handler to remember inputLayerHeight and Number.parseInt(localStorage.getItem('inputLayerHeight')) || 15 to restore the inputLayerHeight at value property of vm.inputLayerHeightSlider object. The same approach can be used for the other values to keep.
Your attempt is almost right. The only thing you need to change is the usage of localStorage. Simply add window or $window (more 'angulary' way to access window variable) variable like so:
$window.localStorage.setItem("networkGraph", JSON.stringify(networkGraph));
Also, I recommend using angular-storage if you're looking for an easy way to work with local storage. It makes things less painful :)
I think the problem might be related to the way you are storing data on your local storage. You are saving data as a string however I think that d3 doesn't recognize strings as valid data options. So instead you should do something like this:
if (sessionStorage) {
// Parse the data to a JavaScript Object
const data = JSON.parse(sessionStorage.getItem("myKey"));
} else {
// Fetch data...
// Set sessionStorage or localStorage
sessionStorage.setItem("myKey", myJSON.toString());
}
You can rearrange the logic as it might suit you but the idea is that in the end you should use JSON.parse() when getting the data from storage.
From https://developers.google.com/web/fundamentals/app-install-banners/#trigger-m68
let deferredPrompt;
window.addEventListener('beforeinstallprompt', (e) => {
e.preventDefault();
// Stash the event so it can be triggered later.
deferredPrompt = e;
});
This code is fine, but I want to trigger the stashed event later, in a different place. To perform that, I need to store an event not just in a variable, but somewhere else.
The question: how can an event be stored with its methods?
I tried Local Storage with serialization/deserialization of an object:
> localStorage.setItem('stashed-event', JSON.stringify(e))
>
> JSON.parse(localStorage.getItem('stashed-event'))
But this approach doesn't work as expected, because it's storing only key-values and losing all event methods.
You cannot store an event in this manner. You want to store an object. Only serializable properties are storable for such an object. Functions are not serializable in JavaScript. Functions are not serializable in many languages.
Fundamentally this is basically because when you deserialize an object, its signature can change. If you have ever programmed in java, this is similar to a deserialization error when reading in a serialized object and attempting to reconstruct an object. Because the body of a method function of an object can change in between the time the object is written to some storage and then later read, methods are not serializable. This is because when you serialize an object, it does not serialize its interface definition where methods are defined. It just stores data.
Same reason when you serialize to a json string, it drops the functions.
Instead of storing an event, store the useful information from the event in an object (or let things be implicitly dropped by stringify and use the event directly).
Which method of storage you use just depends on things not mentioned in your question. Such as how long it should be stored, whether it should be available outside of your site's origin, how much data will typically be stored, whether there is more than one object to store, etc. Based on the limited information provided in your question, you are probably fine just using either localStorage or an in memory array.
If you find the need to store hundreds of objects then indexedDB would begin to be more appropriate. But just choosing a different storage medium will have no effect whatsoever on whether you can store functions. You cannot store functions.
There have been loads of talk around this as soon as I/O 2018 mentioned about handling of A2HS event being developer driven from now onwards. This is also captured in the official doc and inspired from it, there is a beautiful article explaining thoroughly how to achieve exactly this scenario. While I'd suggest to go through the complete article for proper understanding of the updated dynamics around the A2HS flow, feel free to jump onto the "The New Add To Homescreen Flow" section for your requirement.
In a nutshell, follow the following steps:
Create a variable outside the scope of the beforeinstallprompt event handler.
Save a reference to the beforeinstallprompt event object in the above handler.
Use this later to trigger the add to homescreen prompt on demand.
The article have the complete code snippets which you can refer/reuse.
Edit: I read your question once again and realized one important aspect you might be specifically looking for, viz., using it "somewhere else". If this means you are referring to using it on a different page, then my suggestion would be to go for storing the event object in:
IndexedDB which is a collection of "object stores" which you can just drop objects into. Disadvantage - Can have browser compatibility restrictions. Also, can result in large amount of nested callbacks.
Or you can choose to use the "in process cache" (heap memory of your application) which doesn't require serializing either. Disadvantage - This cannot be shared across multiple servers though.
Other than this, I cannot foresee a con free solution at the moment. But will try to figure it out and possibly update the thread.
After reading your question a few times, and the answers another few,
The question: how can any javascript Object be stored with its methods?
The answer: there is no how.
However,
Josh properly explained you can extract and store all the serializable properties, say data, from your event.
I will just add you can create an event with somehow that same data later anywhere, this new event will have all the methods any Event has, but by now probably none of use.
Obviously, even serialized in your data, properties like timeStamp, isTrusted, etc... will be overriden at creating the new event.
What you just miss / need is an EventTarget, the value of the event.target property,
the reference which is lost forever when document.body unloads forever, or when serializing the event Object.
But if it is still alive, or if you know what event.target should be, like a DOM Element or any Object you can reference, from wherever you recreate the event (where?), just dispatch your event to that object, if it listens to that event.type,
your brand new event should be at least heard.
Simple example from MDN EventTarget, or see EventTarget.dispatchEvent
As a comment over the extensive answer by cegfault: eval, and text source code... could be <script> text source code </script>... should your script produces a (String) script. If not you ´d probably better go further backwards to where did your script creates the unserializable things that appear in your event, and think about recreating those things, not the event.
TL;DR to accomplish what you are doing, you have three options:
Store a reference to the event in a global value (which is what most tutorials - like your referenced youtube video - will recommend you do). This requires the event to run in the same context (ie web page) as when you store the reference
When you store the reference to the event in localStorage (such as by name or a key/value look up), on the page/context where you want to execute the event, make sure the appropriate functions and libraries are loaded before executing the event
[strongly NOT recommended] Store the javascript source code in your storate and eval() it later [again, please don't do this]
As mentioned by #Josh and #SaurabhRajpal, what you are asking for, strictly speaking, is not possible in JavaScript. What you are doing with JSON.stringify(e) will probably return undefined or null, as the MDN documentation for JSON.stringify says:
If undefined, a Function, or a Symbol is encountered during conversion it is either omitted (when it is found in an object) or censored to null (when it is found in an array). JSON.stringify can also just return undefined when passing in "pure" values like JSON.stringify(function(){}) or JSON.stringify(undefined).
In short, there is no way to store a single function into localStorage (or any other offline storage). To explain why this is not possible, see this example:
function foo() {
console.log("a")
}
function bar() {
return foo()
}
How can you store bar() for later usage? In order to store bar, you would also have to store foo(). This becomes much more complicated when you consider referencing a function which is in, or uses, a large library (like jQuery, underscore, D3, charting libraries, etc). Keep in mind your computer has already parsed the source code down into binary, and as such won't easily know how to read the function for every possible if, for, and switch statements to ensure all possible correlated functions and libraries are saved.
If you really wanted to do this, you would have to write your own javascript parser, and you really don't want to do that!
So what are your options? First, do everything on the same page, and store the reference to the event in a global value (the youtube video you link to in a comment is using this method).
Your second option is to use a reference to the event (not the event itself), and make sure the source code for that reference is use later. For (html) example:
// on page #1
<script src="path/to/my/js/library.js"></script>
...
<script>
window.addEventListener('beforeinstallprompt', (e) => {
e.preventDefault()
localStorage.setItem('stashed-event', 'before-install')
})
</script>
// later, on page #2:
<script src="path/to/my/js/library.js"></script>
...
<script>
var evt = localStorage.setItem('stashed-event', 'before-install')
if(evt == 'before-install') {
dosomething() // which would be a function in path/to/my/js/library.js
}
// another option here would be to define window listeners for all possible events
// in your library.js file, and then simply build and trigger the event here. for
// more about this, see: this link:
// https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Creating_and_triggering_events
</script>
Finally, you can store javascript source code and then eval() it later. Please, please, please do NOT do this. It's bad practice and can lead to very evil things. But, if you insist:
// on page #1
window.addEventListener('beforeinstallprompt', (e) => {
e.preventDefault()
SomeAjaxFunction("path/to/my/js/library.js", function(responseText) {
localStorage.setItem('stashed-event', {
name: 'before-install',
call: 'beforeInstallFunction()',
src: responseText
})
})
})
// later, on page #2:
var evt = localStorage.setItem('stashed-event', 'before-install')
if(evt) {
console.log("triggering event " + evt.name)
eval(evt.src)
eval(evt.call)
}
Like I said, this is a really bad idea, but it's an option.
IMHO, I think you're trying to avoid including a library or source code in a later page/app/whatever, and javascript just does not work this way. It's best to pass around references in-memory, and only use key/value storage for names. Everything else is a type of coding gymnastics to avoid simply including your source code in the places it needs ot be included.
You can create a global constant and update it when ever event changes rather than serializing it and de-serializing which is a costly processes. SO this is how you can do it - You can create a window instance and clone the event in the window object so that it wont mutate.(Note this wont won't work across tabs)
window.addEventListener('click', (e) => {
e.preventDefault();
window.deferredPrompt = Object.assign(e);//Don't mutate
});
let someOtherMethod = ()=>{
console.log(window.deferredPrompt)
}
window.setInterval(someOtherMethod, 5000);
Try clicking after 5 seconds in the last window and check after 5 seconds
Here is a simple but successful solution.
The idea is to capture the event in a variable and only fire it when signaled by another window of the same origin (domain etc).
The solution uses localStorage methods as the signaling semaphore.
Here is the code I used. I have tested it successfully in Chrome, both mobile & desktop.
//In event handling window
//Register the ServiceWorker
if('serviceWorker' in navigator) {
navigator.serviceWorker.register('sw.js');
};
//Capture beforeInstall event
window.addEventListener('beforeinstallprompt', function(event){
event.preventDefault();
window.deferredPrompt = event;
return false;
})
//Wait for signal
window.onstorage = event => {
if (event.key === 'installprompt') {
//Fire the event when signaled.
window.deferredPrompt.prompt();
// Discard event
window.deferredPrompt = null;
//Discard storage item
localStorage.removeItem('installprompt');
}
}
//In a different window or tab from the same origin fire the event when ready.
localStorage.setItem('installprompt', 'whatever');
Please see if this helps.
Defining an event listener for 'beforeinstallprompt' event
window.addEventListener('beforeinstallprompt', (e) => {
e.preventDefault();
//do all the stufff
console.log('Event triggered');
});
When you want to dispatch the event manually.
Create a new event variable.
var myevent = new Event('beforeinstallprompt');
window.dispatchEvent(myevent);
Outputs 'Event triggered' in the console.
How to create handler on localestorage changed using native javascript?
My try is:
console.log("START");
window.addEventListener('storage',function(e){
if(e.storageArea===sessionStorage){
console.log("storage was changed");
} else {
/* else, event is caused by an update to localStorage, ignore it */
console.log("ELSE");
}
});
localStorage.setItem('qweyxcadsadsadsa', "DSADAS");
console.log("end")
But, it not working, where is a problem?
Thank you for any help!
There is a jsfiddle:
https://jsfiddle.net/1qft6gcb/
You can create your own trigger with setInterval(). On first run, store current values. After that, compare current values with previous, trigger if necessary and update values. I would suggest using an existing pub/sub library for that. Amplify.js encapsulates both local storage and pubsub, but is quite old -mainly because it works very well and doesn't need updates.
I'd really appreciate some help on this, I really can't see my issue here.
For some reason, sensing whether this data (loggedIn) is stored in localStorage with the value "yes" - I've tried the regular way of seeing if the localStorage is empty.
Here's my current code...
<script>
function checkLoggedIn()
{
if (localStorage.getItem("loggedIn") === null) {
alert("empty");
}else{
$(".topbar").html("<span>Saved Jobs(0)</span><span>Welcome, "+ storedUsername +"!</span>");
alert("working");
}
}
</script>
Then obviously I would call this with a body onload. For some reason, I can physically see the value of the localStorage when passing it as a variable, but checking it seems to not be working in the slightest.
I'm using this to simulate functionality of a user logging in, the rest of the functions to handle registration and logging in work fine to actually set the localStorage - so it's not a case of it not being stored.
Thanks for any help given people, it's really appreciated.