It's important to manage the lifecycle of a function to ensure that it resolves
properly. By terminating functions correctly, you can avoid excessive charges
from functions that run for too long or loop infinitely. Also, you can make sure
that the Cloud Functions instance running your function does not shut down
before your function successfully reaches its terminating condition or state.
Use these recommended approaches to manage the lifecycle of your functions:
- Resolve functions that perform
asynchronous
processing (also known as "background functions") by returning a
JavaScript
promise
.
- Terminate
HTTP functions
with
res.redirect()
,
res.send()
, or
res.end()
.
- Terminate a
synchronous
function with a
return;
statement.
Simplify asynchronous code with JavaScript promises
Promises are a modern alternative to callbacks for asynchronous code. A promise
represents an operation and the future value it may return. It also lets you
propagate errors similar to try/catch in synchronous code. You can read about
promises in the Firebase SDK on
The Firebase
Blog
,
and promises in general on
MDN
.
How promises work with functions
When you return a JavaScript promise to a function, that function
keeps running until the promise is resolved or rejected. To indicate that a
function has completed its work successfully, the promise should be resolved. To
indicate an error, the promise should be rejected. This means you only need to
handle errors that you want to.
The following code takes a Firebase Realtime Database
ref
and sets its value to
"world!"
. By returning the result of
set
, your function is guaranteed to
keep running until the asynchronous work of writing the string to the database
is fully completed:
// Always change the value of "/hello" to "world!"
exports.hello = functions.database.ref('/hello').onWrite(event => {
// set() returns a promise. We keep the function alive by returning it.
return event.data.ref.set('world!').then(() => {
console.log('Write succeeded!');
});
});
Examples in context
Most of our Cloud Functions
code
samples
include examples of proper function termination. Here are a few that demonstrate
typical cases: