index.md

Axes

Axes are an integral part of a chart. They are used to determine how data maps to a pixel value on the chart. In a cartesian chart, there is 1 or more X-axis and 1 or more Y-axis to map points onto the 2-dimensional canvas. These axes are known as 'cartesian axes'.

In a radial chart, such as a radar chart or a polar area chart, there is a single axis that maps points in the angular and radial directions. These are known as 'radial axes'.

Scales in Chart.js >v2.0 are significantly more powerful, but also different than those of v1.0.

• Multiple X & Y axes are supported.
• A built-in label auto-skip feature detects would-be overlapping ticks and labels and removes every nth label to keep things displaying normally.
• Scale titles are supported.
• New scale types can be extended without writing an entirely new chart type.

Common Configuration

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Tick Configuration

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Axis Range Settings

Given the number of axis range settings, it is important to understand how they all interact with each other.

The suggestedMax and suggestedMin settings only change the data values that are used to scale the axis. These are useful for extending the range of the axis while maintaining the auto fit behaviour.

let minDataValue = Math.min(mostNegativeValue, options.suggestedMin);
let maxDataValue = Math.max(mostPositiveValue, options.suggestedMax);

In this example, the largest positive value is 50, but the data maximum is expanded out to 100. However, because the lowest data value is below the suggestedMin setting, it is ignored.

let chart = new Chart(ctx, {
    type: 'line',
    data: {
        datasets: [{
            label: 'First dataset',
            data: [0, 20, 40, 50]
        }],
        labels: ['January', 'February', 'March', 'April']
    },
    options: {
        scales: {
            y: {
                suggestedMin: 50,
                suggestedMax: 100
            }
        }
    }
});

In contrast to the suggested* settings, the min and max settings set explicit ends to the axes. When these are set, some data points may not be visible.

Stacking

By default data is not stacked. If the stacked option of the value scale (y-axis on horizontal chart) is true, positive and negative values are stacked separately. Additionally a stack option can be defined per dataset to further divide into stack groups more.... For some charts, you might want to stack positive and negative values together. That can be achieved by specifying stacked: 'single'.

Callbacks

There are a number of config callbacks that can be used to change parameters in the scale at different points in the update process. The options are supplied at the top level of the axis options.

Namespace: options.scales[scaleId]

Name	Arguments	Description
beforeUpdate	axis	Callback called before the update process starts.
beforeSetDimensions	axis	Callback that runs before dimensions are set.
afterSetDimensions	axis	Callback that runs after dimensions are set.
beforeDataLimits	axis	Callback that runs before data limits are determined.
afterDataLimits	axis	Callback that runs after data limits are determined.
beforeBuildTicks	axis	Callback that runs before ticks are created.
afterBuildTicks	axis	Callback that runs after ticks are created. Useful for filtering ticks.
beforeTickToLabelConversion	axis	Callback that runs before ticks are converted into strings.
afterTickToLabelConversion	axis	Callback that runs after ticks are converted into strings.
beforeCalculateTickRotation	axis	Callback that runs before tick rotation is determined.
afterCalculateTickRotation	axis	Callback that runs after tick rotation is determined.
beforeFit	axis	Callback that runs before the scale fits to the canvas.
afterFit	axis	Callback that runs after the scale fits to the canvas.
afterUpdate	axis	Callback that runs at the end of the update process.

Updating Axis Defaults

The default configuration for a scale can be easily changed. All you need to do is set the new options to Chart.defaults.scales[type].

For example, to set the minimum value of 0 for all linear scales, you would do the following. Any linear scales created after this time would now have a minimum of 0.

Chart.defaults.scales.linear.min = 0;

Creating New Axes

To create a new axis, see the developer docs.