tfg-event-context
v1.0.1
Published
Universal Event context for JavaScript
Downloads
458
Readme
event-context
- Work only with NodeJS
- No dependencies
Features
- automatic state passing to downstream functions without explicitly declaring them in functions' parameters (think of React's context but with inheritance). State values are accessible everywhere with
ctx.getState()
- automatic disposal for every pending tasks and event listeners to prevent memory leaks. EventContext works with Promise as well, so you can abort nested unresolved promises with ease. Context disposal is accessible everywhere with
ctx.dispose()
Plugins
EventContext for NodeJS (nextTick, EventEmitter) https://www.npmjs.com/package/tfg-event-context-plugin-node
Installation:
npm i -S tfg-event-context
# to use it with a plugin, just add the plugin package
npm i -S tfg-event-context-plugin-node
Usages
Passing data across functions without declaring them each time.
This is super useful to getting the request that causing an unexpected error. See the example below, it was not easy to get the req inside a downstream function without explicitly passing the req along the way.
import { withContext, getCurrentContext } from 'tfg-event-context';
import { patch } from 'tfg-event-context-plugin-node';
// patch all NodeJS binding after this call
patch();
const server = http.createServer(withContext((req, res) => {
const ctx = getCurrentContext();
const state = ctx.getState();
state.req = req;
handleRequest(req.path, (err, value) => {
res.end(value);
});
}));
function handleRequest(path, callback) {
// do some works with path
process.nextTick(() => {
callDB(callback);
});
}
function callDB(callback) {
try {
somethingWrong();
} catch (ex) {
const ctx = currentContext();
const { req } = ctx.getState();
const { method, url } = req;
console.error('Server Error. Gracefully dying. Request causing error: ', method, url);
}
}
State inheritance
State values are prototypically inherited (think of angular1's scope
).
// initiate contexts
const parent = createContext('parent');
const child = createContext('child');
const pState = parent.getState();
const cState = child.getState();
// state can be set even before running.
pState.parentOnly = 'parentOnly';
pState.shared = 'parentShared';
cState.childOnly = 'childOnly';
cState.shared = 'childOverwrite';
const childComputation = () => setTimeout(() => {
// child
const state = getCurrentContext().getState();
expect(state.childOnly).equal('childOnly');
expect(state.parentOnly).equal('parentOnly');
expect(state.shared).equal('childOverwrite');
done();
}, 10);
const parentComputaion = () => setTimeout(() => {
// parent
child.run(() => {
// child
childComputation()
})
}, 10)
parent.run(() => {
// parent
parentComputaion();
});
Contributions
All contributions are super welcome