deferCallable

deferCallable.js

/**
 * Defer callable. Kinda tricky to explain. Basically:
 *  "Don't make newFn callable until I tell you via this trigger callback."
 *
 * Example:

      // Only start logging after 3 seconds
      var log = function (str) { console.log(str); };
      var deferredLog = deferCallable(log, function (done) {
        setTimeout(done, 3000);
      });

      setInterval(function () {
        deferredLog(Date.now(), 500);
      });

 */
var deferCallable = function (newFn, trigger) {
  var args,
      pointerFn = function () {
        // Initially, the pointer basically does nothing, waiting for the
        // trigger to fire, but we save the arguments that wrapper was called
        // with so that they can be passed to the newFn when it's ready.
        args = [].slice.call(arguments);
      };

  // Immediately call the trigger so that the user can inform us of when
  // the newFn is callable.
  // When it is, swap round the pointers and, if the wrapper was aleady called,
  // immediately call the pointerFn.
  trigger(function () {
    pointerFn = newFn;
    if (args) {
      pointerFn.apply(null, args);
    }
  });

  // Wrapper the pointer function. This means we can swap pointerFn around
  // without breaking external references.
  return function wrapper() {
    return pointerFn.apply(null, [].slice.call(arguments));
  };
};