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JavaScript Basic

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Text lesson

JS Chart.js

Chart.js is a free JavaScript library for creating HTML-based charts. It is among the simplest visualization tools for JavaScript and includes a variety of built-in chart types.

  • Scatter Plot
  • Line Chart
  • Bar Chart
  • Pie Chart
  • Donut Chart
  • Bubble Chart
  • Area Chart
  • Radar Chart
  • Combination Chart

How to Use Chart.js?

1. Include a link to the provided CDN (Content Delivery Network).

<script
src=”https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.js”>
</script>

2. Add a <canvas> to where in the HTML you want to draw the chart:

<canvas id=”myChart” style=”width:100%;max-width:700px”></canvas>

The canvas element should have a distinct id.

Typical Bar Chart Syntax:

const myChart = new Chart(“myChart”, {
  type: “bar”,
  data: {},
  options: {}
});

Typical Line Chart Syntax:

const myChart = new Chart(“myChart”, {
  type: “line”,
  data: {},
  options: {}
});

Bar Charts

js chart

Source Code

const xValues = [“Italy”, “France”, “Spain”, “USA”, “Argentina”];
const yValues = [55, 49, 44, 24, 15];
const barColors = [“red”, “green”,“blue”,“orange”,“brown”];

new Chart(“myChart”, {
  type: “bar”,
  data: {
    labels: xValues,
    datasets: [{
      backgroundColor: barColors,
      data: yValues
    }]
  },
  options: {...}
});

Color a single bar only.

const barColors = [“blue”];

Apply the same color to all bars.

const barColors =“red”;

Color Shades:

const barColors = [
  “rgba(0,0,255,1.0)”,
  “rgba(0,0,255,0.8)”,
  “rgba(0,0,255,0.6)”,
  “rgba(0,0,255,0.4)”,
  “rgba(0,0,255,0.2)”,
];

Horizontal Bars

Simply change the type from “bar” to “horizontalBar”.

type: “horizontalBar”,

Pie Charts

pie chart 1

Example

new Chart(“myChart”, {
  type: “pie”,
  data: {
    labels: xValues,
    datasets: [{
      backgroundColor: barColors,
      data: yValues
    }]
  },
  options: {
    title: {
      display: true,
      text: “World Wide Wine Production”
    }
  }
});

Doughnut Charts

Doughnut charts

Simply change the type from “pie” to “doughnut”.

type: “doughnut”;

Scatter Plots

House Prices vs. Size

scatter plots

Source Code

const xyValues = [
  {x:50, y:7},
  {x:60, y:8},
  {x:70, y:8},
  {x:80, y:9},
  {x:90, y:9},
  {x:100, y:9},
  {x:110, y:10},
  {x:120, y:11},
  {x:130, y:14},
  {x:140, y:14},
  {x:150, y:15}
];

new Chart(“myChart”, {
  type: “scatter”,
  data: {
    datasets: [{
      pointRadius: 4,
      pointBackgroundColor: “rgba(0,0,255,1)”,
      data: xyValues
    }]
  },
  options:{...}
});

Line Graphs

House Prices vs. Size

line graphs

Source Code

const xValues = [50,60,70,80,90,100,110,120,130,140,150];
const yValues = [7,8,8,9,9,9,10,11,14,14,15];

new Chart(“myChart”, {
  type: “line”,
  data: {
    labels: xValues,
    datasets: [{
      backgroundColor:“rgba(0,0,255,1.0)”,
      borderColor: “rgba(0,0,255,0.1)”,
      data: yValues
    }]
  },
  options:{...}
});

By setting the borderColor to zero, you can display the line graph as a scatter plot.

borderColor: “rgba(0,0,0,0)”,

Multiple Lines

multiple lines

Source Code

const xValues = [100,200,300,400,500,600,700,800,900,1000];

new Chart(“myChart”, {
  type: “line”,
  data: {
    labels: xValues,
    datasets: [{
      data: [860,1140,1060,1060,1070,1110,1330,2210,7830,2478],
      borderColor: “red”,
      fill: false
    },{
      data: [1600,1700,1700,1900,2000,2700,4000,5000,6000,7000],
      borderColor: “green”,
      fill: false
    },{
      data: [300,700,2000,5000,6000,4000,2000,1000,200,100],
      borderColor: “blue”,
      fill: false
    }]
  },
  options: {
    legend: {display: false}
  }
});

Linear Graphs

linear graphs 3

Source Code

const xValues = [];
const yValues = [];
generateData(“x * 2 + 7”, 0, 10, 0.5);

new Chart(“myChart”, {
  type: “line”,
  data: {
    labels: xValues,
    datasets: [{
      fill: false,
      pointRadius: 1,
      borderColor: “rgba(255,0,0,0.5)”,
      data: yValues
    }]
  },
  options: {...}
});

function generateData(value, i1, i2, step = 1) {
  for (let x = i1; x <= i2; x += step) {
    yValues.push(eval(value));
    xValues.push(x);
  }
}

Function Graphs

fun graphics

Similar to a linear graph, simply modify the generateData parameter(s).

generateData(“Math.sin(x)”, 0, 10, 0.5);

 

 

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