A quick example

So let's say you want to make a tip calculator.

Getting started with Flocks

You can load Flocks through AMD/CommonJS (node-style) require(), or directly and then fetch it from window. For the micro-example, let's keep it simple, and fetch it from CDN from the global instance. To keep this example extra simple, we'll also keep the controls in their own files, and just load the files from script tags. In a production environment we'd concatenate and uglify instead.

What we'll build

What we'll do is build the calculator step by step. In each heading you'll see a "checkpoint" that points to a Github revision. Those checkpoints are always runable in a browser, and the Github revision pointed to contains the code as the tutorial has gotten to up and until that point.

The text makes you think a little bit about where things go, to help things sink in about how to do the work, but there's always the Github repo to fall back to if you need to take a look at the official state.

Should be pretty straightforward.

We're gonna build an app from scratch, including a modest interactive form.

Let's begin.

HTML boilerplate

First you'll need a simple housing HTML document.

<!doctype html>


    <title>Example Tip Calculator</title>

    <script defer src="http://fb.me/JSXTransformer-0.13.1.js"></script>
    <script defer src="http://fb.me/react-0.13.1.js"></script>
    <script defer src="http://cdnjs.cloudflare.com/ajax/libs/flocks.js/1.6.0/flocks.js"></script>




⛺ Source checkpoint: housing document

This won't do anything but load the two React libraries and the one Flocks library. React will mention in the console logs that you aren't using server-side rendering (duh.)

In the browser, this should white-screen.

Host app

Next, let's make a React component which represents the main application. Initially the control will be trivial; we'll flesh it out as we go, but one thing at a time.

We're going to use the Flocks wrapper for React's .createClass, which just adds the Flocks plumbing mixin to the control for us. This is not a requirement; it's a convenience. Later tutorials will get into the details, but the short version is "that's where .fctx and .fset get set up," which will itself make sense momentarily.

For now, the app.


var TipCalcApp = flocks.createClass({

  render: function() {

    return <div>Basic App!</div>;



We'll also need to add that to <head> as a <script> (in a production system we'd concatenate and uglify instead, but tutorials should stay simple,) like so:

<script type="text/jsx" defer src="TipCalcApp.jsx"></script>

⛺ Source checkpoint: currently unused tipcalc app

But nothing will render yet, because the app isn't being mounted yet. So this will still white-screen.

Mount the app

We like immediate results, don't we?

<script type="text/jsx" defer>

    {target: document.body, control: TipCalcApp},
    {bill: 0, total: 0}


⛺ Source checkpoint: mounted; can see application run

Toss that into <head> also, at the end, and suddenly in-browser you should see "Basic App!".

That just tells Flocks that its configuration is to use the <body> of the document as its mount point, and that its root control should be TipCalcApp; also, that the initial state is for bill and total each to be 0.

You now have a (trivial) working React / Flocks application. Let's make it do stuff.

Layout control

Let's create a basic layout control and get that nonsense out of the way. In the theme of being gross for simplicity, we're just going to make a single <table> with a single <tr> and single <td> to get trivial full centering, then throw a <div> in there with the actual app. No responsive or any such stuff for this tutorial.


var TipCalcLayout = flocks.createClass({

  render: function() {

    return (
      <table id="layout">



Then we can change the render function in TipCalcApp to read

render: function() {
  return <TipCalcLayout>Basic App in layout!</TipCalcLayout>;

And we'll need to add a line to the <head> to include this new control, before the line where it's used:

<script type="text/jsx" defer src="TipCalcLayout.jsx"></script>

⛺ Source checkpoint: now using layout

And now you should see the new text; if you inspect the document in a browser debugger, you'll see there is indeed a <table> there.

Of course, merely having a table doesn't make it do centering for us. For that we'll need to start some CSS.

We'll start with three rules: one that sets both <html> and <body> to fill the client area with no margins, padding, or borders; one that does the same for our table with the id #layout while adding position rules to enforce location; and one which sets vertical-align to middle on the solo <td> in #layout.


html, body {
  height  : 100%;
  width   : 100%;
  padding : 0;
  margin  : 0;
  border  : 0;

#layout {
  position : fixed;
  top      : 0;
  left     : 0;
  right    : 0;
  bottom   : 0;
  height   : 100%;
  width    : 100%;

#layout td {
  vertical-align : middle;

Simple enough. We'll also need to toss a <link> into the <head> to load it:

<link rel="stylesheet" type="text/css" href="TipCalc.css">

⛺ Source checkpoint: we now have vertical centering

Making the app panel

We'll want a panel to contain the stuff so that it looks uniform. It'll have our widgets and behavior on it, because we're keeping things simple and a bit gross for the tutorial.

We'll need an input for the bill amount; three buttons for unhappy, nonplussed, and happy, for tip selection; and a place to put the output text. We can make them attractive later; first we're just going to make it function.

A quick first draft of our UI might look like:


var TipCalcPanel = flocks.createClass({

  render: function() {

    return (

      <div id="panel">

        <label id="amt" for="billAmount">
          Bill amount: $<input id="billAmount"/>

        <div id="howHappy">
          <input type="button" value="25%"/>
          <input type="button" value="20%"/>
          <input type="button" value="15%"/>

        <div id="result">
          Total: $





We'd also need to modify the TipCalcApp to actually use this panel, instead of our dummy text, next:

var TipCalcApp = flocks.createClass({

  render: function() {
    return (


Then we'd need to include the new control in the <head>, again above the control using it:

<script type="text/jsx" defer src="TipCalcPanel.jsx"></script>

⛺ Source checkpoint: rudimentary, terrible-looking panel

It looks awful, but it shows what we need. We'll work on the appearance in a minute; first it's time to make it actually work.

Hooking up the total display

We have two values in our Flocks Context - the bill and the total. The bill is the amount the user is being charged; the total is the amount after the appropriate tip has been added. We've initialized them both to zero, so we are safe to just start displaying them immediately.

Let's hook up the display for total, which currently will only show zero since that's what we've initialized it to, and aren't yet updating it.

's actually really easy. 😁

Remember how we said curly braces { } could add arbitrary javascript? Let's make use of that. In the part of the render function for TipCalcPanel that looks like

<div id="result">
  Total: $

Let's add a block to read out the total member of the Flocks Context.

<div id="result">
  Total: ${this.fctx.total}

⛺ Source checkpoint: First display of information from Flocks Context

That zero that comes out? That's live. It'll update on its own as it needs to. (The dollar sign isn't part of the code. Notice that it renders in the browser. That's just because the bill will be in dollars.)

Let's set up some causes to see that number change.

Hooking up the bill input

We'll need that bill amount to do something too. Relatively straightforward, and we'll cheat a bit to make it immediately visible.

First, let's add a method to the control, so that there's a function label we can give to the form element in a closure. That method will read the current value of the <input> every time it changes, then parse that as a float, then assign that to the bill value in the Flocks Context. (We'll also temporarily assign it to the total just so that we can see the value being set, but that'll get promptly removed because it's not correct.)

Given that TipCalcPanel used to look like

var TipCalcPanel = flocks.createClass({

  render: function() {
    ... whatever ...


Let's now add a method:

var TipCalcPanel = flocks.createClass({

  update: function() {
    var NewBill = parseFloat(document.getElementById('billAmount').value);
    this.fset('bill', NewBill);
    this.fset('total', NewBill); // TEMPORARY AND WRONG

  render: function() {
    ... whatever ...


We'll also need to modify the line with the actual <input> in the render method to call that updater when there's a change. To do that, we write the following:

Bill amount: $<input id="billAmount" onChange={this.update}/>

⛺ Source checkpoint: Working bill update; intentionally wrong total update

The value in { } curly braces will evaluate at creation time to be the member of the component this.update. So, when the input changes, that function will get called. Try it; you'll see the total display change (incorrectly, because the tip isn't yet added.)

Setting the total correctly

So let's stop whining about the total being wrong, and make it right instead. To do that, we need to hook up a way to set it with a given percentage, and we also need to hook up the tipping happiness buttons.

First let's add a method to the control which gives us a nicely formatted number with two mantissa digits:

fmt: function(Tip) {
  return ((this.fctx.bill || 0) * Tip).toFixed(2);

This will take the current bill from the Flocks Context; if bill is something that evaluates to falsey, then it'll common sense substitute zero; then it'll multiply that by the number given as the tip, and return the number formatted to two mantissa digits, which you want for US money.

Next, let's add a handler for the button clicks. Because we need to pass a value in, which means we have to make a call, what'll be on the button is the result of the function, and since that also has to be a function, we'll return a function from this handler (making it actually a handler generator.)

  setTotal: function(Becomes) {
    var fset = this.fset,
        fmt  = this.fmt;
    return function() { fset('total', fmt(Becomes)); };

The reason we assign the two methods to variables then call the variable is that this will be replaced by the time those functions are called, with the event, so this gives us a way to still get at those methods, by passing the variables in through the downwards closure.

Then we need to use the handler generator on the buttons. What was

<input type="button" value="25%"/>
<input type="button" value="20%"/>
<input type="button" value="15%"/>

shall now be

<input type="button" value="25%" onClick={this.setTotal(1.25)}/>
<input type="button" value="20%" onClick={this.setTotal(1.20)}/>
<input type="button" value="15%" onClick={this.setTotal(1.15)}/>

We can also now fix the fake total update. What was

this.fset('total', NewBill); // TEMPORARY AND WRONG

shall now be

this.fset('total', '');

Because when the bill changes, the total should be cleared prior to a new tip being chosen.

⛺ Source checkpoint: Basic functional app

This gives us a basic functional app. However let's make it look better.

Time for some appearance work!

Let's paint the shed a bit.

Buttons, panel centering, and panel width

First, let's fix the width of that panel at 30em, and center it; then let's make those buttons larger, so that they'll be sensible on phones. Also, a gap above the buttons after the first will help with Fitts' Law.

#panel {
  width      : 30em;
  margin     : 0 auto;
  text-align : left;

#howHappy {
  margin : 4em 0;
  width  : 30em;

#howHappy input {
  font-size        : 300%;
  width            : 100%;
  background-color : #f0f0f0;
  border           : thin solid gray;

#howHappy input+input {
  margin-top : 0.5em;

⛺ Source checkpoint: buttons decently styled

Amount row

Next let's increase the size of the text on the amount row, style the input to look a bit better, and get the label to make room.

#amt {
  font-size: 300%;

#amt input {
  font-size           : 100%;
  width               : 4em;
  border              : 0 solid gray;
  border-bottom-width : thin;
  padding-left        : 0.2em;

label {
  display : block;

⛺ Source checkpoint: Amount row styled

Live tips and emoji

Let's make the buttons show the tip amount before you press them; it makes the user feel more in power in real time. Let's also put emoji on the buttons to remind people in-line what they're supposed to do based on their satisfaction.

Both quite straightforward. To add the live calculation means switching the strings to a bit of inline javascript, then using the .fmt method we already made. So,

<input type="button" value="25%" onClick={this.setTotal(1.25)}/>
<input type="button" value="20%" onClick={this.setTotal(1.20)}/>
<input type="button" value="15%" onClick={this.setTotal(1.15)}/>


<input type="button" value={"25% = $" + this.fmt(0.25)} onClick={this.setTotal(1.25)}/>
<input type="button" value={"20% = $" + this.fmt(0.20)} onClick={this.setTotal(1.20)}/>
<input type="button" value={"15% = $" + this.fmt(0.15)} onClick={this.setTotal(1.15)}/>

The important bit is changing value="25%" to value={"25% = $" + this.fmt(0.25)}. One was just a string; the other, because of the { }, is a piece of included javascript which builds a string from a string and a function call.

Then stuffing in emoji is simple, because it's just unicode. Toss it into the first string. Hope you have a modern text editor.

<input type="button" value={"😁 25% = $" + this.fmt(0.25)} onClick={this.setTotal(1.25)}/>
<input type="button" value={"😑 20% = $" + this.fmt(0.20)} onClick={this.setTotal(1.20)}/>
<input type="button" value={"😦 15% = $" + this.fmt(0.15)} onClick={this.setTotal(1.15)}/>

⛺ Source checkpoint: Live values and emoji

Formatting the footer; focus colors

Let's finally format the footer to look nice, and put focus colors on the buttons, to make it more obvious when they're active.

The footer is easy: bigger text, centered, bolded; done.

#result {
  font-size   : 300%;
  font-weight : bold;
  text-align  : center;

Then focus colors are also easy: just set background colors, controlling which input you get with the successor selector, and overriding the previous by specificity:

#howHappy input:focus             { background-color: #e0ffe0; }
#howHappy input+input:focus       { background-color: #ffffe0; }
#howHappy input+input+input:focus { background-color: #ffe0e0; }

⛺ Source checkpoint: footer styling; button focus colors

We're done!

By now, varying on your platform (mostly over fonts and emoji,) you should have something that looks roughly like this:


You can pick up the complete code at the Flocks TipCalc repository.

Next, let's look at some deeper examples. 😁

Fork me on GitHub