lockfn/README.md

Collection of function locking objects.

lockfn
======
**(c)[Bumblehead][0]** [MIT-license](#license)

A collection of function locks through which asynchronous code may be controlled. 

 * [`lockfn.queuing`](#queuing)
 * [`lockfn.caching`](#caching)
 * [`lockfn.expiring`](#expiring) 
 * [`lockfn.rebounding`](#rebounding)
 * [`lockfn.throttling`](#throttling)

[0]: http://www.bumblehead.com                            "bumblehead"


 - <a id="caching"></a>**lockfn.caching**
   Most common lock. Obtain data _once_ for multiple callers.

   A template applied to each item of a list view will be requested _once only_:
   ```javascript
   gettpl = (tplname, fn) => {
     server_request(tplname, (err, tpl) => {
        fn(err, tpl); // tpl is '<b>tpl</b>'
     });
   };
   gettplcache = lockfn.caching((tplname, fn) => {
     gettpl(tplname, fn)
   };
   gettplcache('listitem.mustache', (err, tpl) => {
     console.log('tpl is ' + tpl);        // tpl is <b>item</b>
   });
   gettplcache('listitem.mustache', (err, tplcached) => {
     console.log('tpl is ' + tplcached);  // tpl is <b>item</b>
   });
   ```

   This list uses different templates and _unique_ templates are requested _once only_:
   ```javascript
   // difference between lockfn.caching and lockfn.caching.namespace...
   //
   //   lockfn.caching: the first value obtained is returned to all callers.
   //   if 'lakelistitem.mustache' is obtained first, it is returned to all
   //   callers.
   //
   //   lockfn.caching.namespace: applies caching to values unique to string
   //   param given before the callback. Here 'lakelistitem.mustache' returns a
   //   cached value to calls for 'lakelistitem.mustache'. A different value is
   //   requested and cached for 'countrylistitem.mustache':
   gettplcache = lockfn.caching.namespace((tplname, fn) => {
     gettpl(tplname, fn)
   };
   gettplcache('lakelistitem.mustache', (err, tpl) => {
     console.log('tpl is ' + tpl);       // tpl is <b>lake</b>
   });
   gettplcache('lakelistitem.mustache', (err, tplcached) => {
     console.log('tpl is ' + tplcached); // tpl is <b>lake</b>
   });
   gettplcache('countrylistitem.mustache', (err, ctpl) => {
     console.log('tpl is ' + tpl);       // tpl is <b>country</b>
   });
   gettplcache('countrylistitem.mustache', (err, ctplcached) => {
     console.log('tpl is ' + tplcached); // tpl is <b>country</b>
   });
   ```
 
   Use multiple params with functions returned by `lockfn.caching` and `lockfn.caching.namespace`. Both require a callback as _last_ parameter. `lockfn.caching.namespace` requires a string as the _second-to-last_  parameter (a namespace for which the cache is held).
   ```javascript
   gettplcache = lockfn.caching.namespace((session, cfg, tplname, fn) => {
     gettpl(tplname, fn)
   };
   gettplcache(session, cfg, 'nav.mustache', (err, tpl) => {
     console.log('tpl is ' + tpl);      // tpl is <b>nav</b>
   });
   gettplcache(session, cfg, 'nav.mustache', (err, tplcache) => {
     console.log('tpl is ' + tplcache); // tpl is <b>nav</b>
   });
   gettplcache(session, cfg, 'foot.mustache', (err, tplcache) => {
     console.log('tpl is ' + tplcache); // tpl is <b>foot</b>
   });
   ```

   Clear the cache and request the template anew
   ```javascript
   gettplcache = lockfn.caching.namespace((session, cfg, tplname, fn) => {
     gettpl(tplname, fn)
   };
   session = 'english';
   gettplcache(session, cfg, 'bathroom.mustache', (err, tpl) => {
     console.log(tpl);      // <b>i need the bathroom</b>
   });
   session = 'spanish';
   gettplcache(session, cfg, 'bathroom.mustache', (err, tplcache) => {
     console.log(tplcache); // <b>i need the bathroom</b>
   });
   gettplcache.clear();
   gettplcache(session, cfg, 'bathroom.mustache', (err, tpl) => {
     console.log(tpl);      // <b>puedo ir al bano</b>
   });
   session = 'english';
   gettplcache(session, cfg, 'bathroom.mustache', (err, tpl) => {
     console.log(tpl);      // <b>puedo ir al bano</b>
   });
   ```

 - <a id="expiring"></a>**lockfn.expiring**
   Auto-call a function after given period of time has passed. If a function waits on a response from a server -auto-call that function after a few seconds (and do not allow future calls to the function).
   ```javascript
   lockfn.expiring(function callmeafter5sec () {
     console.log('called in 5 seconds or less');
   }, 5000);
   ```

 - <a id="queuing"></a>**lockfn.queuing**
   Avoid stack overflow. Control caller access to a function that adds numerous frames to the stack by queuing calls so each completes before next begins:
  ```javascript
  getdecryptedblobqueue = lockfn.queuing((cipher, fn) => {
    fn(null, busydecryption(cipher)); // busydecryption adds numerous frames
  });
  getdecryptedblobqueue(cipher, (plain) => {
    console.log(plain); // long string
  });
  getdecryptedblobqueue(cipher, (plain) => {
    console.log(plain); // long string
  }); 
  ```

  Like [`lockfn.caching`](#caching), a callback is required as the _last_ parameter. Other params given in calls to the lock are passed to the function the lock was constructed around.
  ```javascript
  getdecryptedblobqueue = lockfn.queuing((cipher, key, type, fn) => {
    fn(null, busydecryption(cipher, key, type));
  });
  getdecryptedblobqueue(cipher, key, type, (plain) => {
    console.log(plain); // long string
  });
  ```
 
 - <a id="rebounding"></a>**lockfn.rebounding**
   A returned function handles one call, ignoring other calls until the first returns. Useful for handling form submit events, where a form should be submitted once only amid multiple submit events.

   Like [`lockfn.caching`](#caching), a callback is given as the _last_ parameter but is not required.
  ```javascript
  // the following would print 'submit one' only
  rebound = lockrebound((arg1, arg2, exitfn) => {
    setTimeout(function () { 
      console.log('submit one');  // submit one
      exitfn(1, 2) 
    }, 200);
  });
  rebound('a', 'b', (num1, num2) => {
    console.log(num1, num2); // 1 2
  });
  rebound('a', 'b', (num1, num2) => {
    console.log(num1, num2); // not called
  });
  rebound('a', 'b'); // not called
  setTimeout(() => { rebound('a', 'b'); }, 220); // is called
  ```

 - <a id="throttling"></a>**lockfn.throttling**
   A returned function handles first and last calls made within a specified amount of time. Other calls during that time are ignored. Limit calls which may be triggered rapidly many times. For example ,

   The following would print 'rain', 'spain', then 'plain': 
   ```javascript 
   lockthrottle = lockfn.throttling({ ms : 500 });
   lockthrottle(() => { console.log('rain') });  // rain
   lockthrottle(() => { console.log('in') });
   lockthrottle(() => { console.log('spain') }); // spain
   lockthrottle(() => {
     setTimeout(() => {
       console.log('plain') };                         // plain
     }, 600)
   });
   ```
  
---------------------------------------------------------
### <a id="how"></a>How:

Locks here are simple but effective due to the execution model found in [various][1] [ECMAScript][2] environments. Messages are handled in a queue sequentially, protecting the space in one lock call from calls made before or afterward.

[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/EventLoop
[2]: http://nikhilm.github.io/uvbook/eventloops.html


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(The MIT License)

Copyright (c) [Bumblehead][0] <chris@bumblehead.com>

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