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Line · Chart.js documentation

Line

A line chart is a way of plotting data points on a line. Often, it is used to show trend data, or the comparison of two data sets.

Example Usage

var myLineChart = new Chart(ctx, {
    type: 'line',
    data: data,
    options: options
});

Dataset Properties

The line chart allows a number of properties to be specified for each dataset. These are used to set display properties for a specific dataset. For example, the colour of a line is generally set this way.

Name Type Scriptable Indexable Default
backgroundColor Color Yes - 'rgba(0, 0, 0, 0.1)'
borderCapStyle string Yes - 'butt'
borderColor Color Yes - 'rgba(0, 0, 0, 0.1)'
borderDash number[] Yes - []
borderDashOffset number Yes - 0.0
borderJoinStyle string Yes - 'miter'
borderWidth number Yes - 3
cubicInterpolationMode string Yes - 'default'
clip number|object - - borderWidth / 2
fill boolean|string Yes - true
hoverBackgroundColor Color Yes - undefined
hoverBorderCapStyle string Yes - undefined
hoverBorderColor Color Yes - undefined
hoverBorderDash number[] Yes - undefined
hoverBorderDashOffset number Yes - undefined
hoverBorderJoinStyle string Yes - undefined
hoverBorderWidth number Yes - undefined
label string - - ''
lineTension number - - 0.4
order number - - 0
pointBackgroundColor Color Yes Yes 'rgba(0, 0, 0, 0.1)'
pointBorderColor Color Yes Yes 'rgba(0, 0, 0, 0.1)'
pointBorderWidth number Yes Yes 1
pointHitRadius number Yes Yes 1
pointHoverBackgroundColor Color Yes Yes undefined
pointHoverBorderColor Color Yes Yes undefined
pointHoverBorderWidth number Yes Yes 1
pointHoverRadius number Yes Yes 4
pointRadius number Yes Yes 3
pointRotation number Yes Yes 0
pointStyle string|Image Yes Yes 'circle'
showLine boolean - - undefined
spanGaps boolean - - undefined
steppedLine boolean|string - - false
xAxisID string - - first x axis
yAxisID string - - first y axis

General

Name Description
label The label for the dataset which appears in the legend and tooltips.
order The drawing order of dataset. Also affects order for stacking, tooltip, and legend.
xAxisID The ID of the x axis to plot this dataset on.
yAxisID The ID of the y axis to plot this dataset on.

Point Styling

The style of each point can be controlled with the following properties:

Name Description
pointBackgroundColor The fill color for points.
pointBorderColor The border color for points.
pointBorderWidth The width of the point border in pixels.
pointHitRadius The pixel size of the non-displayed point that reacts to mouse events.
pointRadius The radius of the point shape. If set to 0, the point is not rendered.
pointRotation The rotation of the point in degrees.
pointStyle Style of the point. more...

All these values, if undefined, fallback first to the dataset options then to the associated elements.point.* options.

Line Styling

The style of the line can be controlled with the following properties:

Name Description
backgroundColor The line fill color.
borderCapStyle Cap style of the line. See MDN.
borderColor The line color.
borderDash Length and spacing of dashes. See MDN.
borderDashOffset Offset for line dashes. See MDN.
borderJoinStyle Line joint style. See MDN.
borderWidth The line width (in pixels).
clip How to clip relative to chartArea. Positive value allows overflow, negative value clips that many pixels inside chartArea. 0 = clip at chartArea. Clipping can also be configured per side: clip: {left: 5, top: false, right: -2, bottom: 0}
fill How to fill the area under the line. See area charts.
lineTension Bezier curve tension of the line. Set to 0 to draw straightlines. This option is ignored if monotone cubic interpolation is used.
showLine If false, the line is not drawn for this dataset.
spanGaps If true, lines will be drawn between points with no or null data. If false, points with NaN data will create a break in the line.

If the value is undefined, showLine and spanGaps fallback to the associated chart configuration options. The rest of the values fallback to the associated elements.line.* options.

Interactions

The interaction with each point can be controlled with the following properties:

Name Description
pointHoverBackgroundColor Point background color when hovered.
pointHoverBorderColor Point border color when hovered.
pointHoverBorderWidth Border width of point when hovered.
pointHoverRadius The radius of the point when hovered.

cubicInterpolationMode

The following interpolation modes are supported.

  • 'default'
  • 'monotone'

The 'default' algorithm uses a custom weighted cubic interpolation, which produces pleasant curves for all types of datasets.

The 'monotone' algorithm is more suited to y = f(x) datasets : it preserves monotonicity (or piecewise monotonicity) of the dataset being interpolated, and ensures local extremums (if any) stay at input data points.

If left untouched (undefined), the global options.elements.line.cubicInterpolationMode property is used.

Stepped Line

The following values are supported for steppedLine.

  • false: No Step Interpolation (default)
  • true: Step-before Interpolation (eq. 'before')
  • 'before': Step-before Interpolation
  • 'after': Step-after Interpolation
  • 'middle': Step-middle Interpolation

If the steppedLine value is set to anything other than false, lineTension will be ignored.

Configuration Options

The line chart defines the following configuration options. These options are merged with the global chart configuration options, Chart.defaults.global, to form the options passed to the chart.

Name Type Default Description
showLines boolean true If false, the lines between points are not drawn.
spanGaps boolean false If false, NaN data causes a break in the line.

Default Options

It is common to want to apply a configuration setting to all created line charts. The global line chart settings are stored in Chart.defaults.line. Changing the global options only affects charts created after the change. Existing charts are not changed.

For example, to configure all line charts with spanGaps = true you would do:

Chart.defaults.line.spanGaps = true;

Data Structure

The data property of a dataset for a line chart can be passed in two formats.

number[]

data: [20, 10]

When the data array is an array of numbers, the x axis is generally a category. The points are placed onto the axis using their position in the array. When a line chart is created with a category axis, the labels property of the data object must be specified.

Point[]

data: [{
    x: 10,
    y: 20
}, {
    x: 15,
    y: 10
}]

This alternate is used for sparse datasets, such as those in scatter charts. Each data point is specified using an object containing x and y properties.

Stacked Area Chart

Line charts can be configured into stacked area charts by changing the settings on the y axis to enable stacking. Stacked area charts can be used to show how one data trend is made up of a number of smaller pieces.

var stackedLine = new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        scales: {
            yAxes: [{
                stacked: true
            }]
        }
    }
});
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Summary | 1 Annotation
line chart allows a number of properties to be specified for each dataset
2020/06/05 07:08