Javascript is a programming language with a peculiar twist. Its event driven model means that nothing blocks and everything runs concurrently. This is not to be confused with the same type of concurrency as running in parallel on multiple cores. Javascript is single threaded so each program runs on a single core yet every line of code executes without waiting for anything to return. This sounds weird but it's true. If you want to have any type of sequential ordering you can use events, callbacks, or as of late promises.
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function go() { | |
var userId = prompt('Username?', 'Guest'); | |
checkIfUserExists(userId); | |
} | |
var USERS_LOCATION = 'https://SampleChat.firebaseIO-demo.com/users'; | |
function userExistsCallback(userId, exists) { | |
if (exists) { | |
alert('user ' + userId + ' exists!'); |
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# overwrite master with contents of feature branch (feature > master) | |
git checkout feature # source name | |
git merge -s ours master # target name | |
git checkout master # target name | |
git merge feature # source name |
If you use server rendering, keep in mind that neither useLayoutEffect
nor useEffect
can run until the JavaScript is downloaded.
You might see a warning if you try to useLayoutEffect
on the server. Here's two common ways to fix it.
If this effect isn't important for first render (i.e. if the UI still looks valid before it runs), then useEffect
instead.
function MyComponent() {