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This is because you are using V2 of Chart.js while using V3 syntax for the tooltip. This wont work. The options for the tooltip in V2 are placed in a different location:
const options = {
type: 'scatter',
data: {
datasets: [{
label: '# of Votes',
data: [{
x: 0.2505597250394178,
y: 12
},
{
x: 0.1629651642029184,
y: 19
},
{
x: 0.6825862858121792,
y: 3
},
{
x: 0.39821027356939087,
y: 5
},
{
x: 0.1088502186196103,
y: 2
},
{
x: 0.7836566822098099,
y: 3
}
],
backgroundColor: 'orange'
}]
},
options: {
tooltips: {
callbacks: {
label: (ttItem) => (ttItem.value)
}
},
scales: {
yAxes: [{
ticks: {
reverse: false
}
}]
}
}
}
const ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);
<body>
<canvas id="chartJSContainer" width="600" height="400"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.js"></script>
</body>
Source:stackexchange.com