CODEWITHSUNDEEP
javascriptnode.jsasynchronous
n00b
n00b

Reputation: 6360

JS (node.js) - If I make an asynchronous call but do not wait for it to complete will it be guaranteed to complete execution?

Title is long question but if I make an asynchronous call in javascript but do not have a call back or chain it in a promise will it complete execution? i.e. If I have code like:

function markAsInactive(userId) {
    return retrieveUser(userId) // 
    .then(res => {
       const mark = markAsInactive(userId) // returns a promise (say takes 2 seconds)
       return Promise.resolve('blah')
    })
    .then(...etc)
    .catch(...)
}

The call to markAsInactive is fired but the thread does not wait for it to resolve and instead will move on to the next then immediately (is my understanding). Would it be guaranteed to complete execution or would the thread/process cancel the call if the stack returns back to the root?

I know that I can use something like return Promise.all([mark, ...]) to have multiple promises resolve in parallel; this question is more for my edification.

Upvotes: 1

Views: 57

Answers (1)

T.J. Crowder
T.J. Crowder

Reputation: 1075239

Would it be guaranteed to complete execution or would the thread/process cancel the call if the stack returns back to the root?

It completes the call. All asynchronous operations end up exiting the current job (task) before further work on them is done, completely unwinding the stack; it's intrinsic to the job-based nature of JavaScript on a given thread (and NodeJS uses a single thread) and the fact that promise then callbacks are guaranteed to be asynchronous.

The work wouldn't be completed if NodeJS terminated before it was done, but NodeJS keeps running while there are any outstanding tasks, I/O operations, etc.

Upvotes: 2

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