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Svelte/Sapper.js - How to initialize store with localStorage data?

I come from a React background, but I'm switching to Svelte and Sapper for my next application in order to fight the massive bundle size that comes with React these days. However, I'm having trouble initializing Svelte's store with data retrieved from localStorage.
As per the Sapper docs (https://sapper.svelte.dev/docs#Getting_started), I created my project by running npx degit "sveltejs/sapper-template#rollup" my-app from the command line. I then installed the dependencies and removed the demo code in the src folder.
I then created two files: src/routes/index.svelte and src/store/index.js.
Code for both:
src/store/index.js
import {writable} from "svelte/store";
export let userLang;
if(typeof window !== "undefined") {
userLang = writable(localStorage.getItem("lang") || "en");
} else {
userLang = writable(null);
}
src/routes/index.svelte
<script>
import {userLang} from "../store";
</script>
<p>Your Preferred Language: {$userLang}</p>
When I run the application and hit the index route, I see this:
Your Preferred Language: null
which then almost immediately updates and changes to
Your Preferred Language: en
when there is no lang item in localStorage, and changes to
Your Preferred Language: fr
After explicitly setting localStorage.setItem("lang", "fr") from the developer console and refreshing.
I know that the store is being initialized on the server first where window is undefined and then is being rehydrated on the client. So this behavior is expected.
So my question is: how can I skip the server initialization entirely? Is it possible to only set up the store on the client (where localStorage is defined) so that the user's chosen language is immediately available?
I can't default to having everything in English or any other language after the user has chosen to change their preferred language. I also can't get the user language from the browser via navigator.language on initial page load either since navigator is undefined on the server as well.
And having a flash of empty text appear before the store rehydrates would screw up the UX for my application, especially when the value of userLang is going to be used all over the place with translations.
So any strategies or hacks for this are definitely appreciated.
**** Deeper Issue ****
I would actually prefer to not have server-side rendering at all for this application, but I do need all the other excellent features that Sapper provides, like routing, prefetching, and static site building.
So I tried running npx sapper export as per the docs to generate a completely static site in an effort to remove the server from the equation, but the exact same issue still occurs, even though there is no server being used at all.
Does anyone have any advice on how to configure Sapper and turn off SSR but keep the other features?
Thank you!
**** Update ****
As per Rich Harris's answer, wrapping the markup with {#if process.browser} does the trick just fine. So I've updated the src/routes/index.sveltefile like so:
<script>
import {userLang} from "../store";
</script>
{#if process.browser}
<p>Your Preferred Language: {$userLang}</p>
{/if}
And the userLang variable is immediately set with the value from localStorage or defaults to en as I intended for this simple demo. There is no more flash of null, so it's essentially behaving like it's client-side only at this point.
I will work on fleshing out my project and see if there are any more issues I encounter. Til then, I think this solves my issue.

At present, SSR is non-optional. There's an issue open for an SPA mode — https://github.com/sveltejs/sapper/issues/383 — that would behave as you describe, we just need to get round to it.
We also plan to have built-in support for i18n in a future release: https://github.com/sveltejs/sapper/issues/576
In the meantime, you can fake it by wrapping all your markup in {#if process.browser} — anything inside won't be server rendered, but will be present as soon as JavaScript kicks in.

How to get IDFA and ADID on react native?

I want to get the ADID on Android, and IDFA on IOS, how to do this on react native ?
i use this library called react-native-idfa , but the library always said undefined on IDFA

We experienced the same problem. Make sure your iAd.framework is linked the Xcode -> "Build Phases":
They do mention this on their github https://github.com/FreebirdRides/react-native-idfa#podfile
Add AdSupport.framework under "Link Binary With Libraries":
We forked the react-native-idfa if you want to use ours:
https://github.com/FreebirdRides/react-native-idfa
This commit in particular:
https://github.com/FreebirdRides/react-native-idfa/commit/9c6992a53dd109bed41e8c8300906a71e6068043

How to extract GPU information in electron app?

Is there an option to retrieve what graphic card is running on the system (Windows) that does not require usage of chrome://gpu/ ?

From a quick google search, I found a package called systeminfo and it has a function called graphics. It will return an array of graphics controllers and displays which you can filter by the two major vendors (ATI/AMD and nVidia).
Package: https://www.npmjs.com/package/systeminformation

Phonegap 3 contains an alert box in which "OK" crashes browser

I can't come up with a good explanation for this, but when I include
<script type="text/javascript" src="phonegap.js"></script>
In my Phonegap app, which I have not modified, 2 pops will appear on screen.
//The first popup
gap:["PluginManager","startup","PluginManager224542697"]
//the second
gap:["App","show","App224542698"]
I have to cancel both popups and would really love to understand the reasoning.
The two lines in question are on line 21117 and 21118 of phonegap.js
// Tell the native code that a page change has occurred.
require('cordova/exec')(null, null, 'PluginManager', 'startup', []);
require('cordova/channel').onNativeReady.fire();
This of course does not break when its in the app, but it does mean that development is next to impossible.

For me the issue was occurring because phonegap.js was falling back to PROMPT based mode when running outside of phonegap. I believe this mode is intended for phonegap below Android 3.2, where all communication is via alert prompts (which is what you're seeing).
I fixed the problem by setting the following variable before loading phonegap.js:
window._cordovaNative = true;
This tricks phonegap into thinking you're running above phonegap 3.2 hence never enters Prompt mode.
Of course, if you're targeting devices below 3.2 then doing this will probably break all communication with Phonegap on those devices...

I have stumbled upon this error and question while trying the following:
Completed the hello world tutorial with cordova create, etc.
Deployed both on emulator and the connected device w/o a problem.
I got the same error as OP when doing cordova serve and just navigating to //localhost:8000 as instructed.
I agree - seeing those alerts is super annoying. It kills the whole point of speedy non-native js-based development.
What is going wrong?
Communication API with the "device" is falling back to this handler promptbasednativeapi.js (also see cordova-js/src/android/exec.js). On version 3.x.x just saying
window._cordovaNative = true;
was not enough for me. One should implement the whole protocol of communication.
Quick solution
You can use some browser side "emulator", e.g. Ripple emulator extension for chrome ([UPDATE] Consider using https://github.com/apache/incubator-ripple for phonegap 3.x.x as pointed by DuKes0mE). Such an "emulator" can understand and fire respective events, e.g. "device ready". So far it looks promising :-)
What is going on?
An answer by #antscode was of great help. After some digging and reading of cordova/cordova-js code I figured out that
Error comes from the mechanism which is a part of cordova plugin architecture. Plugins are developed as so called cordova commands which can be executed from js - this is exactly how cordova architecture is organized.
Cordova is a JS framework. One is suggested to primary write (non-native) JS code. To talk to all those different native plugins one has to come up with the protocol to communicate with them, sort of RPC with JSON serialization. This is exactly what is going own.
Plugins can be also in pure JS. To quote the manual
Create a new echome plugin with:
window.echo = function(str, callback) {
cordova.exec(callback, function(err) {
callback('Nothing to echo.');
}, "Echo", "echo", [str]);
};
Access it as a cordova command via JS:
window.echo("echome", function(echoValue) {
alert(echoValue == "echome"); // should alert true.
});
No emulator solution
I could imagine a situation when an rather complicated app will break just inside such an web-browser client side "emulator" (and only in it). A better solution would be to figure out a way to convince the app not to fallback to PROMPT method of communication (the one that makes annoying alerts). Well, I do not have such a solution right now :-( Will be happy to learn how to do it though.
Solution is here: https://gist.github.com/ewiger/7d5e0cc8fccf311e9ce2

there is probably no return event for the cancel button. if no instructions are passed to the kernel, this results in an exception(your browser crashing.) try defining an action for the cancel button and see if that helps.

I went into hello/platforms/ios/CordovaLib and copied the cordova.js file into my www root and changed
Or download from here:https://github.com/apache/cordova-ios/blob/master/CordovaLib/cordova.js
<script type="text/javascript" src="phonegap.js"></script>
to
<script type="text/javascript" src="cordova.js"></script>
and no more popups

I was having the same issue with a project created by another developer. The cause in my case was the remains of the Cordova/PhoneGap 2.x configuration. This popup is related to the plugin system. Removing plugin from my config.xml made it better:
<plugin name="InAppBrowser" value="org.apache.cordova.InAppBrowser" />
The end, I decided it would be best to make a new 3.x project and move all of my HTML/CSS/JS to the newly created project. The new project fixed all issues.

I had initially resisted posting an answer on this question. As was mentioned by one of the developers that the phonegap.js should not be included unless it is production code.
This however means you can't tests phonegap features.
To briefly explain my thought process, in all my years developing (php) I have often set global variables that I can easily write code for dev, stage or production.
Please consider this might not be the best way to go, but for me it works and I'm enjoying the rest of my backbone app far more than revisiting this currently ;)
So, I did this:
//Define SD
var SD = {}; //define SD so we can use it globally
/*==================================================
Is Mobile - If true then we are a mobile
================================================== */
SD.isMobile = true;
//This is with the assumtion that your domain contains (for exmaple) http://yourdomain.local
if (document.URL.indexOf("local") > 0 || document.URL.indexOf("sex") > 0) {
SD.isMobile = false;
}
SD = {
isMobile: SD.isMobile,
ENVIROMENT: 'liveApp',
CDN: 'yoururl.com/',
HTTP: 'http://yoururl.com/',
}
// #define the globals depending on where we are -----------------------------------------------------
SD.globals = function () {
switch (window.location.hostname) {
case "sd.local":
SD.ENVIROMENT = 'localApp',
SD.CDN = 'sd.local/',
SD.HTTP = 'http://yoururl.com/',
SD.AJAX = SD.HTTP+'app/';
break;
case "192.168.0.25": //Set to your machines IP address
SD.ENVIROMENT = 'mobilePhone',
SD.AJAX = SD.HTTP+ 'app/';
break;
default:
SD.AJAX = SD.HTTP+'app/';
break;
}
};
And now finally, after all the init work I add the phonegap.js if we need it.
if(SD.isMobile){
$.getScript('phonegap.js', function( data, textStatus, jqxhr){
c( "cordova was loaded." );
});

I was experiencing the exact same two popups you describe but only experienced them when i added iOS to my phonegap project. the first time i did this i copied the www folder from my working Android app. this was the problem because it had artifacts from the Android plugins. After blasting and recreating the iOS app in the phonegap project using the command line tools i more carefully brought over only the needed html, js and css files for my app which resolved the issue.

Reference javax.script.ScriptEngine in android or evaluate a javascript expression

Is it possible to reference the javax.script.ScriptEngine library when developing an android application?
If not is there anyway possible to evaluate a javascript expression in android?

For the classes javax.script.ScriptEngine, javax.script.ScriptEngineFactory and so on, you can add the jsr223.jar to your Android project: just copy the .jar file to your libs directory, and add it from Properties->Java Build Path.
These class will allow your JSR 223-compliant engines to compile. You can then do new SomeScriptEngienFactory().getScriptEngine() to get an engine. I've managed to do this with JNLua 1.0.4 and Rhino 1.7R2.
The file jsr223.jar can be downloaded from http://www.java2s.com/Code/Jar/j/Downloadjsr223jar.htm, a direct link is http://www.java2s.com/Code/JarDownload/jsr223/jsr223.jar.zip.

javax.script.ScriptEngine is not a default part of android, but you could easily jar up any libraries you need(assuming the size is reasonable, I'm not sure) and include them in your project.

According to this post, javax.script.ScriptEngine is not available in Android SDK. You can try the steps below to include the library, but the code may not run, even though it will compile.
Using Android Development Toolkit in Windows, I performed the following steps to get javax.script library.
Right-clicked on the project, went to Properties (Project).
Under the Java Build Path, I chose Libraries tab.
Select Add Library located on the middle right of the Tab
Select JRE System Library under Add Library and click Next...
Select Workspace Default JRE (jre 7)
Click Finish.
Click Ok on the Java Build Path to exist project properties.
Javax.script was then loaded.

If you want to evaluate some code in JS in android
1) to your gradle dependencies add (rhino):
compile 'org.mozilla:rhino:1.7R4'
2) write some code like this to get the result of JS evaluation
Context rhino = Context.enter()
// turn off optimization to work with android
rhino.optimizationLevel = -1
String evaluation = "2+2"
try {
ScriptableProject scope = rhino.initStandardObjects()
String result = rhino.evaluateString(scope, evaluation, "JavaScript", 1, null).toString()
} finally {
Context.exit()
}
3) You can write more complex scripts in JS to run in the android app also (functions etc.)