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Update ticks.callback documentation (#8798)
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@ -17,11 +17,25 @@ Namespace: `options.scales[scaleId].title`, it defines options for the scale tit
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## Creating Custom Tick Formats
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It is also common to want to change the tick marks to include information about the data type. For example, adding a dollar sign ('$'). To do this, you need to override the `ticks.callback` method in the axis configuration.
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In the following example, every label of the Y-axis would be displayed with a dollar sign at the front.
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It is also common to want to change the tick marks to include information about the data type. For example, adding a dollar sign ('$').
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To do this, you need to override the `ticks.callback` method in the axis configuration.
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The method receiver 3 arguments:
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* `value` - the tick value in the **internal data format** of the associated scale.
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* `index` - the tick index in the ticks array.
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* `ticks` - the array containing all of the [tick objects](../api/interfaces/tick).
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The call to the method is scoped to the scale. `this` inside the method is the scale object.
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If the callback returns `null` or `undefined` the associated grid line will be hidden.
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:::tip
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The [category axis](../axes/cartesian/category), which is the default x-axis for line and bar charts, uses the `index` as internal data format. For accessing the label, use `this.getLabelForValue(value)`. [API: getLabelForValue](../api/classes/scale.html#getlabelforvalue)
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:::
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In the following example, every label of the Y-axis would be displayed with a dollar sign at the front.
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```javascript
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var chart = new Chart(ctx, {
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type: 'line',
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@ -41,4 +55,6 @@ var chart = new Chart(ctx, {
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});
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```
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The third parameter passed to the callback function is an array of labels, but in the time scale, it is an array of `{label: string, major: boolean}` objects.
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Related samples:
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* [Tick configuration sample](../samples/scale-options/ticks)
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