JAVASCRIPT for

DATA VISUALIZATION

HELLO!

SONYL NAGALE

• Principal Software Engineer

• > 15 years experience in webdev

• JavaScript Circuit Mentor

• NOT originally a programmer!

AGENDA

Introduction

Why use Javascript

JavaScript 101

D3

INTRODUCTION

I AM...

  • Fluent in JavaScript, PHP, and other Web technologies
  • A full-stack web software engineer
  • Excited about dataviz and its role in consumable data

INTRODUCTION

I Have Experience...

  • Communicating with Design and upper management
  • Analyzing traffic patterns on high-use websites
  • Architecting high availability applications
  • Using D3 and Highcharts to produce dataviz

INTRODUCTION

GOALS

  • Why to use JavaScript for dynamic data
  • JavaScript 101: data types, control structures, and the DOM
  • Collaborative workshop

WHY USE JAVASCRIPT

WHY USE javascript?

WHY USE Javascript

  • Rapidly changing data
  • Programmer-friendly
  • Website-friendly
  • Easily create dashboards and kiosks
  • Interactive
  • Flexible

WHY USE javascript?

Why use javascript

d3: uber rides by neighborhood

Why use javascript

Rapidly changing data

Why use javascript

new Relic

Why use javascript

Pie Charts

Why use javascript

Donut Charts

Why use javascript

Histograms

Why use javascript

Trend Lines

Javascript 101

The basics

  • Values, Operators, Expressions, Keywords, and Comments

  • Semicolon-terminated

  • Common pitfalls:

    • ​Forgetting a semicolon

    • Unbalanced expressions

    • Context

Javascript 101

The basics: Data Types

Boolean
Number
String

Array

 

Null
Undefined

Javascript 101

The basics: Data Types

} What’s the difference?

Boolean
Number
String

Array

 

Null
Undefined

Javascript 101

The basics: variable access


var width = 960,
      height = 500-37;

var margin = {top: 20, right:20, bottom:20, left:50};

Javascript 101

The basics: variable access


var width = 960,
      height = 500-37;

var margin = {top: 20, right:20, bottom:20, left:50};

console.log(width); // 960
console.log(margin.right); // 20

Javascript 101

The basics: Scope


var width = 960,
      height = 500-37;
weight = 100;

var margin = {top: 20, right:20, bottom:20, left:50};


function doStuff() {
    var myVariable = "do stuff";
    weight = 200;
    // do stuff
}

console.log(weight);

Javascript 101

The basics: Scope


var width = 960,
      height = 500-37;
weight = 100;

var margin = {top: 20, right:20, bottom:20, left:50};


function doStuff() {
    var myVariable = "do stuff";
    weight = 200;
    // do stuff
}

doStuff();
console.log(weight);

Javascript 101

The basics: JSON

[
  {
    "time": "1871",
    "Nile": "1120"
  },
  {
    "time": "1872",
    "Nile": "1160"
  },
  {
    "time": "1873",
    "Nile": "963"
  },
  {
    "time": "1874",
    "Nile": "1210"
  },
  {
    "time": "1875",
    "Nile": "1160"
  },
  {
    "time": "1876",
    "Nile": "1160"
  }
]

Javascript 101

The basics: JSON

  • Key-Value pairs
  • Objects...
  • ... inside an Array
[
  {
    "time": "1871",
    "Nile": "1120"
  },
  {
    "time": "1872",
    "Nile": "1160"
  },
  {
    "time": "1873",
    "Nile": "963"
  },
  {
    "time": "1874",
    "Nile": "1210"
  },
  {
    "time": "1875",
    "Nile": "1160"
  },
  {
    "time": "1876",
    "Nile": "1160"
  }
]

Javascript 101

The Arcana: Everything is an Object

Object notation

var myObject = {
    x : 1,
    y : 2,

    getX: function() {
        return this.x;
    }
};

console.log(myObject.getX());

Javascript 101

The Arcana: Everything is an Object

Object notation

String.prototype.foo = function() {
    return "bar";
}

var unga = "Hello";

console.log(unga);
console.log(unga.foo());

Javascript 101

The Basics: control structures

text += cars[0] + "<br>"; 
text += cars[1] + "<br>"; 
text += cars[2] + "<br>"; 
text += cars[3] + "<br>"; 
text += cars[4] + "<br>"; 
text += cars[5] + "<br>";

REPETITION!!!

Javascript 101

The Basics: control structures

For loops: DRY

for (i = 0; i < cars.length; i++) { 
    text += cars[i] + "<br>";
}

Javascript 101

The Basics: control structures

Nested Loops

Javascript 101

The Basics: The Dom

<!DOCTYPE html>
<html>
<head>
    <title>Page Title</title>
</head>
<body>

<h1 id="heading">This is a Heading</h1>
<p class="paragraph">This is a paragraph.</p>

</body>
</html>

Document Object Model!

Javascript 101

The Basics: CSS

<!DOCTYPE html>
<html>
<head>
    <title>Page Title</title>
</head>
<body>

<h1 id="heading">This is a Heading</h1>
<p class="paragraph">This is a paragraph.</p>

</body>
</html>

Just a smidge...

Javascript 101

The Basics: CSS

<!DOCTYPE html>
<html>
<head>
    <title>Page Title</title>
</head>
<body>

<h1 id="heading">This is a Heading</h1>
<p class="paragraph">This is a paragraph.</p>

</body>
</html>

Just a smidge...

#heading
.paragraph

Javascript 101

The Basics: THE DOM

OK, so back to the DOM

D3

d3!

D3

d3js.org

“D3 allows you to bind arbitrary data to a Document Object Model (DOM), and then apply data-driven transformations to the document. For example, you can use D3 to generate an HTML table from an array of numbers. Or, use the same data to create an interactive SVG bar chart with smooth transitions and interaction.”

D3

d3 and Selections

var paragraphs = document.getElementsByTagName("p");
for (var i = 0; i < paragraphs.length; i++) {
  var paragraph = paragraphs.item(i);
  paragraph.style.setProperty("color", "white", null);
}

D3

d3 and Selections

var paragraphs = document.getElementsByTagName("p");
for (var i = 0; i < paragraphs.length; i++) {
  var paragraph = paragraphs.item(i);
  paragraph.style.setProperty("color", "white", null);
}
$("p").css("color","white");

jQuery

D3

d3 and Selections

var paragraphs = document.getElementsByTagName("p");
for (var i = 0; i < paragraphs.length; i++) {
  var paragraph = paragraphs.item(i);
  paragraph.style.setProperty("color", "white", null);
}
$("p").css("color","white");
d3.selectAll("p").style("color", "white");

jQuery

d3

D3

d3 and Selections

Lorem ipsum!

D3

d3 and Selections

Lorem ipsum!

D3

d3 and Web Standards

  • HTML
  • CSS
  • SVG

D3

d3: Bar Chart

var width = 420,
    barHeight = 20;

var x = d3.scale.linear()
    .range([0, width]);

var chart = d3.select(".chart")
    .attr("width", width);

d3.tsv("data.tsv", type, function(error, data) {
  x.domain([0, d3.max(data, function(d) { return d.value; })]);

  chart.attr("height", barHeight * data.length);

  var bar = chart.selectAll("g")
      .data(data)
    .enter().append("g")
      .attr("transform", function(d, i) { return "translate(0," + i * barHeight + ")"; });

  bar.append("rect")
      .attr("width", function(d) { return x(d.value); })
      .attr("height", barHeight - 1);

  bar.append("text")
      .attr("x", function(d) { return x(d.value) - 3; })
      .attr("y", barHeight / 2)
      .attr("dy", ".35em")
      .text(function(d) { return d.value; });
});

function type(d) {
  d.value = +d.value; // coerce to number
  return d;
}

THANK YOU!

Sonyl Nagale

sonyl@nagale.com

JavaScript for Data Visualization, 02/13/2017

By Sonyl Nagale

JavaScript for Data Visualization, 02/13/2017

  • 20

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