According to the docs there is a onClick handler for the legend exposing the event object. If you stopPropagation it stops the data series hiding:
let chart = new Chart(elem.find('canvas')[0], {
type: 'line',
data: {
labels: [],
datasets: []
},
options: {
responsive: true,
maintainAspectRatio: false,
legend: {
onClick: (e) => e.stopPropagation()
}
}
});
The above is ES6, if your not using a supported browser below is the older ES5 equivilant.
legend: {
onClick: function (e) {
e.stopPropagation();
}
}
Chartjs must register its own click event after the legend.onClick which is why this stop it executing.
docs