How to put labels at 4 points of the day? - chart.js

Question

This question is two-fold (two ways to solve)
I want to make a chart that plots 24 hours worth of data, not starting at midnight, and with ticks (and associated grid) at the four cardinal points of the day.
I don't care if the x axis is 'time' or anything else, as long as it looks fine. I've seen a category chart with the labels arbitrarily shifted, but I can only reproduce this with one data point per label, and this needs multiple data points between the labels. If I label all the data points I don't know how to skip labels such that only "0:00', '6:00', '12:00', and '18:00' are visible.
It's supposed to look like this:
This is how far I've come:
function generateData() {
function randomNumber(min, max) {
return Math.random() * (max - min) + min;
}
function randomPoint(date) {
return {
t: date.valueOf(),
y: randomNumber(0, 100)
};
}
var date = moment("2000-01-01T"+"08:30");
var now = moment();
var data = [];
while (data.length <=48) {
data.push(randomPoint(date));
date = date.clone().add(30, 'minute')
}
return data;
}
var cfg = {
data: {
datasets: [{
label: 'CHRT - Chart.js Corporation',
backgroundColor: 'red',
borderColor: 'red',
data: generateData(),
type: 'line',
pointRadius: 0,
fill: false,
lineTension: 0,
borderWidth: 2
}]
},
options: {
scales: {
xAxes: [{
type: 'time',
time: {
round: 'minute',
unit: 'minute',
stepSize: 360,
displayFormats: {
minute: 'kk:mm'
}
}
}],
yAxes: [{
gridLines: {
drawBorder: false
}
}]
},
tooltips: {
intersect: false,
mode: 'index'
}
}
};
var chart = new Chart('chart1', cfg);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.3/Chart.min.js"></script>
<canvas id="chart1" height="60"></canvas>
The problem here is that the first tick is at 08:30 not at 12:00.
I've tried to set the min value of the axis, but this either shifts part of the data out of view (min: moment("2000-01-01T12:00")), or creates a gap before the data starts (min: moment("2000-01-01T06:00")), both of which are unacceptable.
function generateData() {
function randomNumber(min, max) {
return Math.random() * (max - min) + min;
}
function randomPoint(date) {
return {
t: date.valueOf(),
y: randomNumber(0, 100)
};
}
var date = moment("2000-01-01T"+"08:30");
var now = moment();
var data = [];
while (data.length <=48) {
data.push(randomPoint(date));
date = date.clone().add(30, 'minute')
}
return data;
}
var cfg = {
data: {
datasets: [{
label: 'CHRT - Chart.js Corporation',
backgroundColor: 'red',
borderColor: 'red',
data: generateData(),
type: 'line',
pointRadius: 0,
fill: false,
lineTension: 0,
borderWidth: 2
}]
},
options: {
scales: {
xAxes: [{
type: 'time',
time: {
round: 'minute',
unit: 'minute',
stepSize: 360,
displayFormats: {
minute: 'kk:mm'
}
},
ticks: {
min: moment("2000-01-01T06:00"),
}
}],
yAxes: [{
gridLines: {
drawBorder: false
}
}]
},
tooltips: {
intersect: false,
mode: 'index'
}
}
};
var chart = new Chart('chart1', cfg);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.3/Chart.min.js"></script>
<canvas id="chart1" height="60"></canvas>

Answer 1

Took me some time, but I think I got the answer.
You can define the ticks with and display them with options.scales.xAxes[0].ticks.source = 'labels', but the hardest part was to get the next timestamp of 0:00, 6:00, 12:00 or 18:00.
That's why the code for the first label is quite complex. If you want to know anything, just let me know and I can explain it.
Should work with any time you want.
Complete code (same as JSBin with preview here):
let data = {
datasets: [{
label: 'CHRT - Chart.js Corporation',
backgroundColor: 'red',
borderColor: 'red',
type: 'line',
pointRadius: 0,
pointHoverRadius: 0,
fill: false,
lineTension: 0,
borderWidth: 2,
data: []
}]
}
function randomNumber(min, max) {
return Math.round(Math.random() * (max - min) + min)
}
// temp variable for data.datasets[0].data
let datasetData = []
// Fill first dataset
datasetData[0] = {
x: moment("2000-01-01T08:30"),
y: randomNumber(0, 100)
}
// Fill remaining datasets
for (let i = 1; i < 48; i++) {
datasetData[i] = {
x: moment(datasetData[i-1].x).add(30, 'minutes'),
y: randomNumber(0, 100)
}
}
data.datasets[0].data = datasetData
// Fill first label
data.labels = [
moment(datasetData[0].x).hour(moment(datasetData[0].x).hour() + (6 - moment(datasetData[0].x).hour() % 6) % 6).minutes(0)
]
// Fill remaining labels
for (let i = 1; i < 4; i++) {
data.labels.push(moment(data.labels[i-1]).add(6, 'hours'))
}
let options = {
responsive: true,
scales: {
xAxes: [{
type: 'time',
time: {
unit: 'hour',
displayFormats: {
hour: 'kk:mm'
}
},
ticks: {
source: 'labels'
}
}],
yAxes: [{
gridLines: {
drawBorder: false
}
}]
},
tooltips: {
intersect: false,
mode: 'index',
callbacks: {
title: function(tooltipItem, data) {
return moment(tooltipItem[0].label).format('YYYY-MM-DD, HH:mm')
}
}
}
}
let chart = new Chart('chart1', {
type: 'line',
data: data,
options: options
});