_shortOut.js

/** Used to detect hot functions by number of calls within a span of milliseconds. */
var HOT_COUNT = 800,
    HOT_SPAN = 16;

/* Built-in method references for those with the same name as other `lodash` methods. */
var nativeNow = Date.now;

/**
 * Creates a function that'll short out and invoke `identity` instead
 * of `func` when it's called `HOT_COUNT` or more times in `HOT_SPAN`
 * milliseconds.
 *
 * @private
 * @param {Function} func The function to restrict.
 * @returns {Function} Returns the new shortable function.
 */
function shortOut(func) {
  var count = 0,
      lastCalled = 0;

  return function() {
    var stamp = nativeNow(),
        remaining = HOT_SPAN - (stamp - lastCalled);

    lastCalled = stamp;
    if (remaining > 0) {
      if (++count >= HOT_COUNT) {
        return arguments[0];
      }
    } else {
      count = 0;
    }
    return func.apply(undefined, arguments);
  };
}

module.exports = shortOut;