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Ben Nadel
On User Experience (UX) Design, JavaScript, ColdFusion, Node.js, Life, and Love.

Code Kata: Creating A Fluent, Closure-Based "Builder" API In Lucee CFML

By Ben Nadel on
Tags: ColdFusion

As of late, I've been feeling very creatively blocked. Right now, work is taking every ounce of mental energy that I have, which is leaving me with little left over with which to create magic. As such, I just wanted to do something - anything - to create a little neural activity to keep the old brain-meat lubricated. I thought it might be fun to experiment with a fluent, closure-based "builder" API in Lucee CFML

Whether or not you know it, you are almost certainly familiar with what a "fluent" API is. If you've used jQuery, you've used a fluent API. A fluent API is one that depends heavily on method-chaining. For example, in jQuery, you might see something like:

jQuery( "div.items" ).first().addClass( "selected" )

The key to a fluent API is that many of the methods return a reference back to an API rather than a null or void value.

For this code kata, I'm going to create a "builder" API, which is a "fluent" API in which a series of methods work together to create some sort of aggregate value. And, in this case, that aggregate value is going to be a URL. So, the builder API will expose methods for defining parts of that URL independently, followed by a .build() method which will collapse the independent parts down into a final value: the URL.

Here's what I came up with - it's not perfect, it's just a little fun to get my brain working:


			.withProtocol( "//" )
			.withHost( "" )
			.withPath( "/people" )
			.withParam( "bff" )
			.withParam( "filter", "cool beans" )

	echo( "<br />" );

			.withPath( "people" )
			.withParam( "bff" )

	// ------------------------------------------------------------------------------- //
	// ------------------------------------------------------------------------------- //

	* I return a builder that can construct a URL from its various parts. Calling
	* .build() will flatten all the components down into a string.
	public struct function urlBuilder() {

		var protocol = "";
		var host = "";
		var path = "";
		var searchParams = [];

		// As we define MOST of our API methods, we want them to implicitly return a
		// reference back to the API itself so that the interface can be fluent (ie, rely
		// on method-chaining). However, so as not to have to do this in every SETTER,
		// this utility method will proxy any callback that is passed to it.
		var makeFluent = ( required function callback ) => {

			var fluentProxy = () => {

				callback( argumentCollection = arguments );
				return( builderApi );


			return( fluentProxy );


		// Define the public API of our fluent builder.
		var builderApi = {
			withProtocol: makeFluent(( required string newProtocol ) => {

				protocol = newProtocol;

			withHost: makeFluent(( required string newHost ) => {

				// Strip-off any trailing slash - it will be deferred to the path.
				host = newHost.reReplace( "[\\/]+$", "", "one" );

			withPath: makeFluent(( required string newPath ) => {

				// Ensure leading slash.
				path = ( newPath.left( 1 ) == "/" )
					? newPath
					: ( "/" & newPath )

			withParam: makeFluent(( required string key, string value ) => {

				// NOTE: A NULL value will be encoded as a key-only parameter.
				searchParams.append([ key, ( value ?: nullValue() ) ]);

			// The BUILD method will flatten all the URL components down into a string.
			build: () => {

				var parts = [];

				if ( protocol.len() ) {

					parts.append( protocol );


				if ( host.len() ) {

					parts.append( host );


				if ( path.len() ) {

					parts.append( path );


				// Flatten the search parameters down into a string.
				var searchString = searchParams
						( tuple ) => {

							if ( tuple.isDefined( 2 ) ) {

								return( encodeForUrl( tuple[ 1 ] ) & "=" & encodeForUrl( tuple[ 2 ] ) );

							} else {

								return( encodeForUrl( tuple[ 1 ] ) );


					.toList( "&" )

				if ( searchString.len() ) {

					parts.append( "?" );
					parts.append( searchString );


				return( parts.toList( "" ) );


		return( builderApi );



As you can see, the urlBuilder() function returns a Struct that is our API. Now, each method in the API could have returned the builderApi reference directly; but, again, my goal here was to have some fun and experiment. So, instead of having the explicit return, I'm proxying each API method through a makeFluent() function, which invokes the API method and then returns the API reference implicitly.

Now, if we run this ColdFusion code, we get the following output:



As you can see, the .build() method collapsed all of the independent URL components down into a single URL string.

There's not much more to say - this was just a fun experiment. It wasn't meant to be super robust. I'm not even saying that I would recommend doing this kind of thing with Closures (as opposed to an instantiated ColdFusion Component). It's just good to play with aspects of the Lucee CFML language.

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