A throttling function

throttle.js

(function ( global ) {

	'use strict';

	var throttle;

	if ( typeof Date.now !== 'function' ) {
		Date.now = function () {
			return new Date().getTime();
		};
	}

	throttle = function ( fn, options ) {
		var active, timeout, nextAllowed, scheduled;

		if ( typeof options !== 'object' ) {
			options = {
				delay: options
			};
		}

		if ( !options.delay ) {
			options.delay = 250; // default value is 250 milliseconds
		}

		return function () {
			var args, timeNow, call, context;

			args = arguments;
			timeNow = Date.now();

			context = options.context || this;

			call = function () {
				fn.apply( context, args );
				
				nextAllowed = Date.now() + options.delay;
				scheduled = false;
			};

			// if it's been less than [delay] since the last call...
			if ( timeNow < nextAllowed ) {
				// schedule a call, if one isn't already scheduled
				if ( !scheduled ) {
					setTimeout( call, nextAllowed - timeNow );
					scheduled = true;
				}
			}

			else {
				call();
			}
		};
	};

	// export as CommonJS module...
	if ( typeof module !== 'undefined' && module.exports ) {
		module.exports = throttle;
	}

	// ... or as AMD module...
	else if ( typeof define !== 'undefined' && define.amd ) {
		define( function () { return throttle; });
	}

	// ... or as browser global
	else {
		global.throttle = throttle;
	}

}( typeof window !== undefined ? window : this ));