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Fix/category scale wrong tooltip #12106

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Fix/category scale wrong tooltip #12106

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d326efc
Add test for category scale getLabelForValue
mbehr1 Aug 2, 2025
2c2d06c
Fix category scale returning wrong labels for string values
mbehr1 Aug 2, 2025
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2 changes: 1 addition & 1 deletion src/scales/scale.category.js
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ const validIndex = (index, max) => index === null ? null : _limitValue(Math.roun
function _getLabelForValue(value) {
const labels = this.getLabels();

if (value >= 0 && value < labels.length) {
if (typeof value === 'number' && value >= 0 && value < labels.length) {
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The function should be used to use the internal values of the category scale and convert them to the string values.
The internal values are numbers. This feels like a wrong implementation of this function.

The type definition also specifies the input as a number and not a string
https://www.chartjs.org/docs/latest/api/classes/Scale.html#getlabelforvalue

I would find it more logical that there would be a guard against number inputs but that would possible be too breaking since inputting a number as a string will be seen as a number.

So the current implementation is the most correct in my eyes and this is not a bug.

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@LeeLenaleee but then the issue is here:

Chart.js/src/core/core.datasetController.js

Line 694 in 6372280

value: vScale ? '' + vScale.getLabelForValue(parsed[vScale.axis]) : '' 

  getLabelAndValue(index) {
    const meta = this._cachedMeta;
    const iScale = meta.iScale;
    const vScale = meta.vScale;
    const parsed = this.getParsed(index);
    return {
      label: iScale ? '' + iScale.getLabelForValue(parsed[iScale.axis]) : '',
      value: vScale ? '' + vScale.getLabelForValue(parsed[vScale.axis]) : ''
    };
  }

?

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Do you have a reproducible sample of the issue. Because I don't see the issue.
When I add a label with a number in it it just shows the label on the correct spot, even though indexed it would have picked something else.

https://jsfiddle.net/Lrkc75ao/

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Will add one. Currently I see this in my vscode extension but a small example doesn't show the issue. Will keep on analyzing.

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@LeeLenaleee
see a minimal example here (was struggling as the code I tried to repro with had my change already.... ;-)
https://jsfiddle.net/9xefs4g1/1/

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image

here a pic of the example. Example code:

var options = {
  type: 'line',
  data: {
    labels: ["Jan", "2", "Mar", "Apr", "May", "Jun", "Jul"],
    datasets: [
			{
        type: 'line',
				data: [{x: 0, y: 'ON'},
        {x: 1, y: 'OFF'},
        {x: 2, y: '0'},
        {x: 3, y: 0},
        {x: 4, y: '1'}],
				borderWidth: 1,
        parsing: false
			}
		]
  },
  options: {
    scales: {
      y: {
        type: 'category',
        indexAxis: 'x',
        labels: ['ON', 'OFF', '1', '0'],
      },
    },
  }
}

var ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);

return labels[value];
}
return value;
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4 changes: 3 additions & 1 deletion test/specs/scale.category.tests.js
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,7 @@ describe('Category scale tests', function() {
yAxisID: 'y',
data: [10, 5, 0, 25, 78]
}],
labels: ['tick1', 'tick2', 'tick3', 'tick4', 'tick5']
labels: ['tick1', 'tick2', 'tick3', '1', 'tick5']
},
options: {
scales: {
Expand All @@ -176,6 +176,8 @@ describe('Category scale tests', function() {
var scale = chart.scales.x;

expect(scale.getLabelForValue(1)).toBe('tick2');
expect(scale.getLabelForValue('tick3')).toBe('tick3');
expect(scale.getLabelForValue('1')).toBe('1'); // and not 'tick2'
});

it('Should get the correct pixel for a value when horizontal', function() {
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