pretty simple on-off interface for continuously running a function over a given interval (if specified)

continuous.js

/*
  answer for Tim Evko @tevko re https://twitter.com/Tevko/status/572698827548839936
  March 3, 2015
  
  continuous()
  + calls a function fn continuously every (optional) interval milliseconds
  + provides on-off or pause-resume switch
*/

function continuous(fn, interval) {
  
  // The strategy is to create a middleman function that 
  // + holds on to the runnable {fn} function via closure
  // + returns itself as the API with on and off methods.
  
  typeof interval != 'number' && (interval = 0);

  var runnable = fn;
  var timeout; // or requestID
  
  // when fn is a function it will be called repeatedly
  // until middle.off(); is called
  
  function middle(fn) {
    
    runnable = fn;
    timeout = window.clearTimeout(timeout); // or cancelAnimationFrame(requestID)

    // if runnable is callable...
    typeof runnable == 'function' && 
      (timeout = window.setTimeout(function run() { // or requestID = requestAnimationFrame(function run...)
        
        runnable(); // runnable wraps whatever real logic we want
        middle.on(); // ready for next
        
      }, interval));
    
    return middle;
  }
  
  // resume
  middle.on = function on() {
    //console.log('on');
    return middle(fn);
  }
  
  // pause
  middle.off = function off() {
    console.log('off');
    return middle(null);
  }
  
  return middle;
}


/***** test *****/

// this wraps whatever logic you'd really want to execute
function runnable () {
  console.log('running');
}

// optional call interval (defaults to 0 in continuous())
var interval = 50;

// create continuous instance
var m = continuous(runnable, interval);

// start calling runnable continuously untile we call m.off();
m.on();

// demonstrate on-off switch using planned timeouts
setTimeout(m.off, 250);
setTimeout(m.on, 500);
setTimeout(m.off, 750);

/*
should see:

running
running
running
running
off
running
running
running
running
off

*/