Flot - Documentation

What is Flot?

Flot is a pure JavaScript plotting library for jQuery, designed for producing simple yet elegant line, bar, and pie charts within web applications. It’s lightweight, easy to use, and highly customizable, making it a popular choice for quickly integrating interactive data visualization into web projects. Flot focuses on providing a clean and straightforward API, minimizing the learning curve for developers. Its reliance on jQuery simplifies integration into existing jQuery-based projects.

Key Features and Benefits

Setting up Flot: Installation and Dependencies

Flot requires jQuery. You can download both libraries from their respective websites or use a package manager like npm or yarn.

Using a CDN: The easiest way to include Flot is through a Content Delivery Network (CDN). Include the jQuery library first, followed by the Flot library:

<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/flot/jquery.flot.min.js"></script>

Using npm: If you are using npm, install Flot and jQuery:

npm install jquery flot

Then, in your JavaScript file, require them appropriately (the specific syntax will depend on your module bundler):

// Example using a module bundler like Webpack
const $ = require('jquery');
require('flot');

Basic Usage Example

This example creates a simple line chart:

<!DOCTYPE html>
<html>
<head>
<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/flot/jquery.flot.min.js"></script>
</head>
<body>
<div id="placeholder" style="width:600px;height:300px;"></div>

<script>
$(function () {
    var data = [
        [0, 10],
        [1, 20],
        [2, 15],
        [3, 25]
    ];
    $.plot($("#placeholder"), [data]);
});
</script>
</body>
</html>

This code snippet includes jQuery and Flot via CDN, then uses $.plot() to create a chart within the div with the ID “placeholder”. The data array provides the x and y coordinates for the line. Remember to adjust paths to your library files if not using CDNs.

Basic Plotting

Creating a Simple Line Chart

Creating a line chart with Flot is straightforward. You provide the plotting data as an array of points, and Flot handles the rendering.

$(function () {
    var data = [
        [0, 10], [1, 20], [2, 15], [3, 25], [4, 30]
    ];

    $.plot("#placeholder", [data]);
});

This code creates a line chart with the given data points. Replace "#placeholder" with the ID of your target div element. The data is an array of [x, y] coordinate pairs.

Creating a Bar Chart

To create a bar chart, you use the same $.plot() function, but you need to specify the series.bars option within the options object:

$(function () {
    var data = [
        [0, 10], [1, 20], [2, 15], [3, 25], [4, 30]
    ];

    $.plot("#placeholder", [data], {
        series: {
            bars: {
                show: true,
                barWidth: 0.6 // Adjust bar width as needed
            }
        }
    });
});

This adds bars to the chart. barWidth controls the width of the bars (0.6 is a common value). Other options within series.bars allow further customization (e.g., align, fill).

Creating a Pie Chart

Pie charts require a slightly different data structure. Each data point should be an object with a label and a data value:

$(function () {
    var data = [
        { label: "Series A", data: 10 },
        { label: "Series B", data: 20 },
        { label: "Series C", data: 15 }
    ];

    $.plot("#placeholder", data, {
        series: {
            pie: {
                show: true
            }
        }
    });
});

This creates a pie chart. The label property is used for the slice labels, and data represents the value.

Data Format and Structure

Flot accepts data in different formats, depending on the chart type:

For more complex scenarios (e.g., multiple datasets, time series), the data structure can be more elaborate; refer to the Flot documentation for advanced options.

Axis Configuration: Labels, Ranges, and Tick Formatting

You can customize the axes using the xaxis and yaxis options within the $.plot() options object:

$(function () {
    var data = [[0, 10], [1, 20], [2, 15], [3, 25]];

    $.plot("#placeholder", [data], {
        xaxis: {
            ticks: [[0, "Jan"], [1, "Feb"], [2, "Mar"], [3, "Apr"]], //Custom ticks
            min: 0, //Set minimum value
            max: 3 //Set maximum value
        },
        yaxis: {
            min: 0,
            max: 30,
            tickFormatter: function (val, axis) {
                return val + "°C"; //Custom tick formatting
            }
        }
    });
});

This example customizes x-axis ticks with month labels, sets axis ranges, and adds a degree Celsius suffix to the y-axis ticks using a custom tickFormatter.

Legends and Titles

Legends and titles enhance chart readability. You can enable legends automatically, or customize their placement and appearance. Titles require a bit more manual work using HTML elements:

$(function () {
  // ... your plot data and options ...

  $.plot("#placeholder", [data], options);  //options as defined above

  // Add title manually (Flot doesn't directly support titles)
  $("#placeholder").before("<div style='font-size:1.2em; font-weight:bold;'>My Chart Title</div>");

});

This adds a title above the chart. For legends, simply include legend: { show: true } within your options object to enable Flot’s automatic legend generation. Further legend options allow controlling position, background, and more.

Advanced Plotting Techniques

Multiple Axes and Plots

Flot allows you to create plots with multiple axes (e.g., a secondary y-axis) and combine multiple plots within a single container. For multiple axes, you specify yaxis and y2axis options (and corresponding data series linked to each axis):

$(function () {
    var data1 = [[0, 10], [1, 20], [2, 15]];
    var data2 = [[0, 50], [1, 60], [2, 55]];

    $.plot("#placeholder", [
        { data: data1, yaxis: 1 },
        { data: data2, yaxis: 2 }
    ], {
        yaxes: [{}, {
            position: 'right',
            alignTicksWithAxis: 1
        }]
    });
});

This creates a plot with two y-axes; data1 uses the primary y-axis (yaxis: 1, default), and data2 uses the secondary (yaxis: 2). Note the yaxes configuration for positioning and alignment. Multiple plots in one container require careful management of the plot’s dimensions and data series.

Interactive Zooming and Panning

Flot supports interactive zooming and panning using the zoom and pan options. Enabling these requires specifying appropriate options and handling the plotselected event:

$(function () {
    var options = {
        zoom: { interactive: true },
        pan: { interactive: true },
        selection: { mode: "xy" }
    };

    var plot = $.plot("#placeholder", [data], options);  //data is your data array

    $("#placeholder").bind("plotselected", function (event, ranges) {
        plot.setSelection(ranges);
    });
});

This enables interactive zooming and panning. The plotselected event fires when the user selects a region (through zooming/panning), allowing you to update the plot accordingly. The selection option defines the selection mode (“xy” for both axes).

Highlighting Data Points

Highlighting data points on mouseover requires handling the plothover event:

$(function () {
    var plot = $.plot("#placeholder", [data]); // data is your data array

    $("#placeholder").bind("plothover", function (event, pos, item) {
        if (item) {
            $("#tooltip").html(item.datapoint[1]) //Show y-value in tooltip
                .css({ top: item.pageY + 5, left: item.pageX + 5 })
                .fadeIn(200);
        } else {
            $("#tooltip").hide();
        }
    });
});

This example shows a simple tooltip containing the y-value on hover. You’ll need a <div id="tooltip"></div> element in your HTML for this to work. More sophisticated highlighting can involve changing point colors or sizes.

Customizing Tooltips

Building upon the highlighting example, you can customize tooltips to display any relevant information from your data:

// ... inside plothover event handler ...
$("#tooltip").html("X: " + item.datapoint[0] + "<br>Y: " + item.datapoint[1] + "<br>Series: " + item.series.label)
// ...

This displays x-value, y-value, and series label in the tooltip. You can add any other data associated with the data point.

Working with Time Series Data

Flot handles time series data effectively. You need to use JavaScript’s Date object for the x-values:

$(function () {
    var data = [
        [new Date(2024, 0, 1), 10],
        [new Date(2024, 0, 8), 20],
        // ... more data points
    ];

    $.plot("#placeholder", [data], {
        xaxis: {
            mode: "time",
            timeformat: "%m/%d" // Customize time format
        }
    });
});

The mode: "time" option in xaxis is crucial. timeformat controls how time values are displayed on the x-axis.

Using Different Chart Types in One Plot

You can combine different chart types in a single plot by creating an array of series with different options:

$(function () {
    var data1 = [ ...line chart data...];
    var data2 = [ ...bar chart data...];

    $.plot("#placeholder", [
        { data: data1, lines: { show: true } },
        { data: data2, bars: { show: true } }
    ]);
});

This combines line and bar charts. Each series object specifies its own chart type options.

Plotting Large Datasets: Performance Optimization

Plotting very large datasets can impact performance. Flot provides options to optimize:

Remember that optimizing for large datasets involves finding the right balance between visual representation and performance based on your specific data and hardware capabilities.

Customization and Styling

Series Options: Colors, Lines, Markers, and Fillings

Flot offers extensive options to customize the appearance of individual data series. These options are specified within the series object in the $.plot() options.

$(function () {
    var data = [ ... your data ... ];

    $.plot("#placeholder", [data], {
        series: {
            color: "#007bff", // Set a specific color
            lines: { show: true, lineWidth: 2, fill: 0.2 }, // Customize lines
            points: { show: true, radius: 3, fillColor: "#ffffff" }, // Customize points
            bars: { show: false } // disable bars if needed
        }
    });
});

This example shows how to set series color, line width, filling, point radius and point color. You can adjust fill (0-1) for the line fill opacity. Many other options exist within lines, points, and bars to control appearance. For multiple datasets, you can specify these options for each series individually within the data array.

Grid Customization: Background, Lines, and Markings

The plot’s grid can be customized extensively. Options are defined within the grid option.

$(function () {
    var data = [ ... your data ... ];

    $.plot("#placeholder", [data], {
        grid: {
            backgroundColor: { colors: ["#fff", "#eee"] }, // Two-color gradient background
            borderColor: "#ccc", // Border color
            borderWidth: 1,
            hoverable: true, // Enable hover effects
            clickable: true,  // Enable click effects
            autoHighlight: true, // Highlight on hover automatically
            markings: [ // Add markings to the grid
                { xaxis: { from: 1, to: 2 }, color: "#faa" },
            ]
        }
    });
});

This example shows how to set a gradient background, border, enables hover and click effects, and adds a highlighted marking to a section of the grid. markings allows creating horizontal or vertical highlighted regions.

Axis Customization: Tick Placement, Labels, and Rotation

Axis appearance is customizable via xaxis and yaxis options.

$(function () {
    var data = [ ... your data ... ];

    $.plot("#placeholder", [data], {
        xaxis: {
            ticks: [ [0,"Zero"], [1,"One"], [2,"Two"] ], // Custom ticks and labels
            tickColor: "#999", // Tick color
            tickLength: 5, // Tick length
            tickFormatter: function (val, axis) { return val * 10; }, // custom formatting function
            rotateTicks: 45 // Rotate x-axis labels by 45 degrees.
        },
        yaxis: {
            min: 0,
            max: 100,
            tickDecimals: 2 // Two decimal places on y-axis ticks
        }
    });
});

This example demonstrates setting custom ticks and labels, tick color, length, and custom formatting function. rotateTicks rotates labels for improved readability (particularly useful for long labels on x-axis).

Theme and Styling Options

Flot itself doesn’t directly support themes, but you can achieve themed appearances through CSS and by consistently applying the options described above across your charts. Creating a JavaScript object containing common plot options and applying this to multiple chart initializations will make it easier to maintain a consistent style across your application.

Using CSS for Styling

While many aspects are controlled via Flot’s options, you can enhance styling using CSS. Target elements like the plot container (#placeholder), axes, and legend elements. For instance:

#placeholder {
    font-family: sans-serif; /* Customize font */
}

.flot-xaxis-label {
    font-weight: bold;  /* Customize x-axis label style */
}

CSS offers granular control over fonts, colors, and overall presentation. Note the class names used for axis labels, which are subject to potential changes, so consult the Flot documentation for the most up-to-date class names.

Creating Custom Plugins

Flot’s extensibility is achieved through plugins. Creating a plugin involves writing a JavaScript function that adds new functionality or options to Flot. This often involves adding new methods to the $.plot function or modifying existing ones. A comprehensive guide on plugin development would require a separate, detailed section beyond the scope of this manual’s introduction. Consult the official Flot documentation and examples for detailed information about plugin creation.

Plugins and Extensions

Overview of Available Plugins

Flot’s core functionality can be extended significantly through plugins. While Flot’s core is relatively lean, a vibrant community has developed several plugins to add features not included in the base library. These plugins often provide capabilities like:

Finding available plugins often involves searching online repositories like GitHub. The official Flot website may also list or link to some popular plugins. Be sure to check the plugin’s compatibility with your Flot version.

Integrating and Using Plugins

Plugin integration usually involves including the plugin’s JavaScript file in your HTML after including the Flot library and jQuery:

<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/flot/jquery.flot.min.js"></script>
<script src="path/to/your/plugin.js"></script>  <!-- Path to your plugin -->

After including the plugin, its functionality should be automatically available. The specific usage will depend on the plugin’s documentation. Many plugins add new options to the $.plot() function’s options object or introduce entirely new functions. Consult the plugin’s documentation for specific instructions on how to use its features.

Developing Custom Plugins

Creating a custom Flot plugin involves extending Flot’s functionality to add new features. This is generally done by registering a new plugin with Flot, adding new options, and potentially modifying the internal plotting behavior. While the specifics depend on the plugin’s complexity, the fundamental steps often include:

  1. Create a JavaScript file: This file will contain your plugin’s code.

  2. Define the plugin function: This function will typically register the plugin with Flot and define its options and functionality. It might add new options to the $.plot options object, or modify how data is processed or rendered.

  3. Register the plugin: Use Flot’s plugin registration mechanism (usually a call to $.plot.plugins.push()) to register your plugin with Flot.

  4. Add new functionality: This might involve creating new methods within the $.plot object or extending existing methods.

  5. Handle options: Properly handle the plugin’s options within your plugin function.

  6. Testing: Thoroughly test your plugin to ensure it works correctly and integrates seamlessly with Flot.

Developing plugins requires a good understanding of Flot’s internal workings and JavaScript object-oriented programming. The official Flot documentation (if available) may provide more advanced information about plugin development. Referencing existing plugins and examining their code can provide valuable insight into plugin architecture and implementation details. Creating a robust plugin requires good testing and documentation practices.

API Reference

This section provides a concise overview of Flot’s core API. For complete details and a comprehensive list of options, refer to the full Flot documentation (if available). Note that specific option names and functionalities may vary slightly depending on the Flot version.

$.plot Function

The core function for creating a plot is $.plot(). It takes three primary arguments:

$.plot(placeholder, data, options);

The $.plot function returns a plot object that can be used to interact with the plot after it has been rendered (e.g., for zooming, panning, or accessing data).

Options Object

The options object is a key part of customizing Flot plots. It contains numerous properties grouped into categories like series, xaxis, yaxis, grid, legend, etc. Some commonly used options include:

Series Options

Series-specific options determine how each dataset is rendered. They are often specified within the series option.

These options are frequently used to adjust line styles, point sizes, bar widths, and other visual aspects of individual datasets. They can be defined globally in the series option or individually for each dataset within the data array.

Axis Options

Axis options control the appearance and behavior of the x and y axes (xaxis and yaxis).

Grid Options

Grid options control the background and lines of the plot area.

Legend Options

Legend options control the display of the legend.

Events and Callbacks

Flot supports several events that you can listen for using jQuery’s .bind() method (or the more modern .on()). Key events include:

These events typically pass information about the event’s location and data point (if applicable) to the callback function. Using these events allows you to implement interactive features such as tooltips, zooming, and data point highlighting. Consult the full Flot documentation for specific details on the arguments passed to each callback.

Remember that this is a simplified overview. Consult the complete Flot API documentation for detailed descriptions of all options, methods, and events. The specifics may differ depending on the Flot version.

Troubleshooting and FAQs

Common Errors and Solutions

This section addresses some common issues encountered when using Flot.

Debugging Tips

Frequently Asked Questions

This FAQ section is not exhaustive, and new questions may arise depending on the specific application and the Flot version used. Refer to the online Flot documentation and community forums for more detailed answers and further assistance.