vue-chartjs: is it possible to dynamically change color based on value - vue-chartjs

Question

Using vue-chartjs is it possible to change to color of the bar?
This is similar to this question which is based on chart.js
chart.js bar chart color change based on value, and the jsfiddle provided in the answer is exactly what I'm looking for, except within vue-chartjs.
Any help appreciated

Answer 1

So this should be your chart calling (in my case, I named it bar-chart)
<bar-chart
:chart-data="barData"
:options="barChartOptions">
</bar-chart>
:chart-data and :options are 2 props defined when I create my bar component:
Vue.component('bar-chart', {
extends: VueChartJs.Bar,
props: ['chartData', 'options'],
So your barData, should be an object like this:
{datasets: [...], labels: [...]}
Your dataset is an array with the charts you want to show. So if you want to show only 1 data, than your array only has one position. So let's assume that by now. We'll use dataset = dataset[0]
Your dataset accepts some properties, 2 of them are a must:
Data (an array with the data you want to show)
Label (the name of the label when you hover on the bardata. It should display "Label: value"
It also accepts some other properties like:
fill
hoverBackgroundColor
backgroundColor
check more here: https://www.chartjs.org/docs/latest/charts/bar.html
so now, your backgroundColor property is either a color value (e.g. red, #FF0000), or an array.
If it is an array, then this should be true dataset.bgColors.length === dataset.data.length
and each dataset.bgColors array position is the color of the respective value in the dataset.data array.
dataset: {
data: [1,2,-3,-4,2,1]
backgroundColor: ['green', 'green', 'red', 'red', 'green', 'green']
...
}
So now, you can just build a bgColors array with the color you want, based on your data.
------------- UPDATING THE DATA -----------------
To anybody else who is looking for a way to UPDATE your chart data after it was rendered. It's a different question, but to help the community:
When you set your chart component, you can define a watch for the chartData prop, so when the chartData changes, the method is called and you re-render the chart:
Vue.component('bar-chart', {
extends: VueChartJs.Bar,
props: ['chartData', 'options'],
methods: {
renderLineChart () {
this.renderChart(this.chartData, this.options)
}
},
mounted () {
this.renderLineChart()
},
watch: {
chartData: function () {
this.$data._chart.destroy()
this.renderLineChart()
}
}
})
IMPORTANT: Make sure you make a new copy of the new chartData object info because the watch will only check if the object itself changed, not its inner properties.
However, if you really want to change ONLY the dataset.data or dataset.backgroundColor or any other, than the watcher will not know it changed. You can use the property deep: true in the watcher for this, as it will check changes deep inside the chartData object:
watch:
chartData: {
handler: function () {
this.$data._chart.destroy()
this.renderLineChart()
},
deep: true
}
}
I hope the answer was clear for everyone.
Best regards