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golike-defer
Advanced tools
go's defer statement in JavaScript
defer()
is a function decorator which injects a $defer()
function
as a first parameter.
This injected function can be used to register deferreds, functions
which will be executed at the end of the decorated function execution,
no matter how it ended (via a return
or a throw
).
Note: the deferreds are executed in the reverse order of their declarations.
Installation of the npm package:
> npm install --save golike-defer
import { defer } from 'golike-defer'
const fn = defer(
// Works both with sync and async functions
async function($defer, ...args) {
$defer(() => {
console.log("always called at the end of the function");
});
$defer.onFailure(() => {
console.log("called at the end of the function only on failure");
});
$defer.onSuccess(() => {
console.log("called at the end of the function only on success");
});
}
);
Context and arguments can be passed to the deferred function:
$defer(cb)
: called without context nor arguments$defer(cb, arg1, arg2)
: called with arguments arg1
and arg2
$defer.call(thisArg, cb)
: called with context thisArg
$defer.call(thisArg, 'method')
: thisArg.method
called with context thisArg
import { defer } from 'golike-defer'
import fs from 'fs'
const readFileSync = defer(($defer, path) => {
const fd = fs.openSync(path, 'r')
// The file will be automatically closed at the end of the function,
// whether it succeed or failed.
$defer(fs.closeSync, fd)
const { size } = fs.statSync(path)
const buffer = Buffer.allocUnsafe(size)
fs.readSync(fd, buffer, 0, buffer.length)
return buffer
})
// Helper to promisify a function call.
const fromCallback = fn => new Promise((resolve, reject) => {
fn((error, result) => error ? reject(error) : resolve(result))
})
const readFile = defer(async ($defer, path) => {
const fd = await fromCallback(cb => fs.open(path, 'r', cb))
// The file will be automatically closed at the end of the function,
// whether it succeed or failed.
$defer(() => fromCallback(cb => fs.close(fd, cb)))
const { size } = await fromCallback(cb => fs.stat(path, cb))
const buffer = Buffer.allocUnsafe((size)
await fromCallback(cb => fs.read(fd, buffer, 0, buffer.length, cb))
return buffer
})
Exceptions (or rejected promises) thrown in deferred are caught and printed on the console.
This can be customized with the onError()
method:
const myDefer = defer.onError(error => {
log(error);
});
const fn = myDefer(($defer, arg1, arg2) => {
// ...
});
# Install dependencies
> npm
# Run the tests
> npm test
# Continuously compile
> npm run dev
# Continuously run the tests
> npm run dev-test
# Build for production (automatically called by npm install)
> npm run build
Contributions are very welcomed, either on the documentation or on the code.
You may:
ISC © Julien Fontanet
FAQs
go's defer statement in JavaScript
We found that golike-defer demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 3 open source maintainers collaborating on the project.
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