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    event-context

    0.5.4 • Public • Published

    event-context

    • Event context for JavaScript
    • Work in both NodeJS and browsers
    • No dependencies

    Features

    1. 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()
    2. 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 jQuery (jQuery events) https://www.npmjs.com/package/event-context-plugin-jquery

    EventContext for NodeJS (nextTick, EventEmitter) https://www.npmjs.com/package/event-context-plugin-node

    Installation:

    npm i -S event-context
     
    # to use it with a plugin, just add the plugin package 
    npm i -S 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 'event-context';
    import { patch } from '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();
    });
     

    Auto unbinding

    When you decide to stop all event listeners created in an context, just call ctx.dispose()

    const ctx = getCurrentContext();
    ctx.dispose()

    All bound event handlers within the context will be removed.

    Contributions

    All contributions are super welcome

    Install

    npm i event-context

    DownloadsWeekly Downloads

    1

    Version

    0.5.4

    License

    ISC

    Last publish

    Collaborators

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