How to create a simple JavaScript percentage graph (or chart)

Ciprian on Monday, April 11, 2022 in JavaScript Arrays & Objects, JavaScript DOM

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Graphs on a table
Graphs on a table by Markus Spiske is licensed under CC-CC0 1.0

This small JavaScript snippet creates percentage graphs out of raw (array) data. Just input the name/value pairs of the involved graph elements, and leave the rest to the snippet. The values can be either absolute or percentage.

You can render more than one graph on the same page by invoking the graph function multiple times, with different array parameters.

Since the first example is created using absolute values, the script also displays the total value at the end.

What we will build

Here is a demo of both versions:

How to use

See below two versions of the JavaScript snippet, the first requiring that the graph values be absolute (e.g., 35, 123), while the second, in percentage (e.g., 25%, 75%).

Let’s add the required HTML elements:

<h3>This is an absolute values graph</h3>
<div id="graph-1"></div>

<h3>This is a percentage values graph</h3>
<div id="graph-2"></div>

Absolute Values Version

This version will automatically calculate percentages for all your values, based on the total number.

let graphx = [];

graphx[0] = ['Apples', 60];
graphx[1] = ['Pears', 75];
graphx[2] = ['Strawberries', 24];
graphx[3] = ['Bananas', 52];

function graphit(g, g_width, g_element) {
    let total = 0,
        calpercentage = 0,
        calwidth = 0;

    for (i = 0; i < g.length; i++) {
        total += parseInt(g[i][1]);
    }

    let output = '<table border="0" cellspacing="0" cellpadding="8">';

    for (i = 0; i < g.length; i++) {
        calpercentage = Math.round((g[i][1] * 100) / total);
        calwidth = Math.round(g_width * (calpercentage / 100));

        output += `<tr><td>${g[i][0]}</td><td><svg xmlns="http://www.w3.org/2000/svg" width="${calwidth}" height="10"><g class="bar"><rect width="${calwidth}" height="10"></rect></g></svg> ${calpercentage}%</td></tr>`;
    }

    output += '</table>';

    g_element.innerHTML = `${output}<br>Total fruits: <b>${total}</b>`;
}

graphit(graphx, 200, document.getElementById('graph-1')); // 200 is the maximum width of the graph, in pixels

Percentage Values Version

let graphv = [];

graphv[0] = ['Cranberries', 28];
graphv[1] = ['Redberries', 36];
graphv[2] = ['Blueberries', 30];
graphv[3] = ['Raspberries', 6];
graphv[4] = ['Strawberries', 80];
graphv[5] = ['Blackberries', 11];
graphv[6] = ['Lingonberries', 24];
graphv[7] = ['Cloudberries', 98];

function graph_it_percentage(g, g_width, g_element) {
    let output = '<table border="0" cellspacing="0" cellpadding="8">',
        calwidth_percentage = 0;

    for (i = 0; i < g.length; i++) {
        calwidth_percentage = g_width * (parseInt(g[i][1]) / 100);

        output += `<tr><td>${g[i][0]}</td><td><svg xmlns="http://www.w3.org/2000/svg" width="${calwidth_percentage}" height="10"><g class="bar"><rect width="${calwidth_percentage}" height="10"></rect></g></svg> ${g[i][1]}%</td></tr>`;
    }

    output += '</table>';

    g_element.innerHTML = output;
}

graph_it_percentage(graphv, 200, document.getElementById('graph-2')); // 200 is the maximum width of the graph, in pixels

Note that I have used an SVG for the bar, which can be easily coloured or styled as a gradient.

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