Chart.js - add gradient instead of solid color - implementing solution

The link you provided was pretty clear, you have to put in the field fillColor in datasets as linearGradient object instead of a plain color. You can do complex gradients, but here is the code of a simple one (changing the opacity of the same orange):

var gradient = ctx.createLinearGradient(0, 0, 0, 400);
gradient.addColorStop(0, 'rgba(250,174,50,1)');   
gradient.addColorStop(1, 'rgba(250,174,50,0)');

And your complete datasets :

datasets: [
  {
    fillColor: gradient, // Put the gradient here as a fill color
    strokeColor: "#ff6c23",
    pointColor: "#fff",
    pointStrokeColor: "#ff6c23",
    pointHighlightFill: "#fff",
    pointHighlightStroke: "#ff6c23",
    data: [
      25.0, 32.4, 22.2, 39.4, 34.2, 22.0,
      23.2, 24.1, 20.0, 18.4, 19.1, 17.4
    ]
  }
]

See it in action in this JSFiddle

Note: For those people who is using newer version (v2.7.0) of Chart.js, find out that is not working while you're copy-paste @bviale's answer back to your code base; Some property names has changed:

fillColor -> backgroundColor
strokeColor -> borderColor
pointColor -> pointBackgroundColor
pointStrokeColor -> pointBorderColor

You will need to update those property names to make it work.

Reference: https://github.com/chartjs/Chart.js/blob/master/docs/charts/line.md#dataset-properties

For using it in react, I did the following way.

You need to pass an id to your component and then fetch the element using that id.

import React, { Component } from 'react'
import { Line } from 'react-chartjs-2'

export default class GraphComponent extends Component {
  constructor(props) {
    super(props)
    this.state = {
      chartData: {}
    }
  }

  componentDidMount() {
    // your code
    var ctx = document.getElementById('canvas').getContext("2d")
    var gradient = ctx.createLinearGradient(0, 0, 0, 400)
    gradient.addColorStop(0, 'rgba(229, 239, 255, 1)')
    gradient.addColorStop(1, '#FFFFFF')
    const newData = {
      labels: [1, 1],
      datasets: [
        {
          label: 'usd',
          data: [1,1],
          backgroundColor: gradient,
          borderColor: this.props.border_color,
          pointRadius: 0
        }
      ]
    }
    this.setState({chartData: newData})
  }

  // more of your code

  render() {
    return(
      <Line
        id='canvas' // you need to give any id you want
        data={this.state.chartData}
        width={100}
        height={30}
        options={{
          legend: {
            display: false
          }
        }}
      />
    )
  }
}

This is only my second answer so please forgive me if I have made any mistakes in writing.

for latest version do not forget to set fill: true

  function getGradient(ctx, chartArea) {
    let gradient = ctx.createLinearGradient(
      0,
      chartArea.bottom,
      0,
      chartArea.top
    );
    gradient.addColorStop(0.9, "rgba(102, 235, 169, .4)");
    gradient.addColorStop(0, "transparent");
    return gradient;
  }

set dataset options as below

fill: true,
backgroundColor: function (context) {
    const chart = context.chart;
    const { ctx, chartArea } = chart;

   // This case happens on initial chart load
   if (!chartArea) return;
   return getGradient(ctx, chartArea);
},

Updated version 2022

var ctx = document.getElementById("temp-chart").getContext("2d");

declare gradient after getting context element i.e ctx

var gradient = ctx.createLinearGradient(0, 0, 0, 400);
            gradient.addColorStop(0.2, 'rgb(255, 10, 86,0.5)');
            gradient.addColorStop(1, 'rgb(255, 10, 86,0.1)');

and your dataset will be

datasets: [{
                 label: 'Transactions',
                 data: [1,3,4,5]
                 backgroundColor: gradient,
                 borderColor: 'rgb(255, 10, 86,1)',
                 borderWidth: 2,
           }],

The React solutions posted here may work with some effort but will most likely produce additional errors such as "createLinearGradient is not a function" or "document.getElementById() returning null" because it is looking for the chart id before the DOM has loaded. It doesn't help that ChartJS documentation for React is lacking.

I find a cleaner solution is to create the charts as a functional component and make sure all needed ChartJS assets are properly initialized.

1. Making sure ChartJS is properly initialized and registered

import { Line } from 'react-chartjs-2' import { Chart as ChartJS, CategoryScale, LinearScale, PointElement, LineElement, Title, Tooltip, Legend, Filler, ScriptableContext } from "chart.js";

ChartJS.register(CategoryScale,LinearScale,PointElement,LineElement,Title,Tooltip,Legend,Filler);

2. Using the ScriptableContext to add the gradient

backgroundColor: (context: ScriptableContext<"line">) => { const ctx = context.chart.ctx; const gradient = ctx.createLinearGradient(0, 0, 0, 200); gradient.addColorStop(0, "rgba(238,174,202,1)"); gradient.addColorStop(1, "rgba(238,174,202,0)"); return gradient; },

Live Codepen w/ Line Chart Gradient enter link description here

You could use this npm package.

https://www.npmjs.com/package/chartjs-plugin-gradient

This makes it very easy to create a gradient backgroundColor or borderColor.

Example:

const chart = new Chart(ctx, {
  data: {
    datasets: [{
      // data
      gradient: {
        backgroundColor: {
          axis: 'y',
          colors: {
            0: 'red',
            50: 'yellow',
            100: 'green'
          }
        },
        borderColor: {
          axis: 'x',
          colors: {
            0: 'black',
            1: 'white',
            2: 'black',
            3: 'white'
          }
        }
      }
    }]
  }
});

For anyone using Angular and ng2-charts, here is my solution. Chart setup was left out for brevity.

import { Component, OnInit, ViewChild, ChangeDetectorRef, AfterViewInit } from '@angular/core';
import { BaseChartDirective } from 'ng2-charts';
import { GenericLineChart } from './generic-line-chart';


@Component({
    selector: 'app-stats-chart',
    templateUrl: './stats-chart.component.html',
    styleUrls: ['./stats-chart.component.scss']
})
export class StatsChartComponent implements OnInit, AfterViewInit {
    @ViewChild(BaseChartDirective, { static: true }) chartDirective: BaseChartDirective;

    constructor(private changeDetectorRef: ChangeDetectorRef) { }

    ngOnInit() {
        // ...setup chart
    }

    ngAfterViewInit() {
        // set gradient
        const gradient = this.chartDirective.chart.ctx.createLinearGradient(0, 0, 0, 400);
        gradient.addColorStop(0, 'rgba(30, 214, 254, .3)');
        gradient.addColorStop(1, 'rgba(0,0,0,0)');
        this.chart.lineChartData[0].backgroundColor = gradient;

        this.changeDetectorRef.detectChanges();
    }

}