Mon 21 Jul 22:43:21 CEST 2025

js/ui/chart/docs/axes/labelling.md

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+# Labeling Axes
+
+When creating a chart, you want to tell the viewer what data they are viewing. To do this, you need to label the axis.
+
+## Scale Title Configuration
+
+The scale label configuration is nested under the scale configuration in the `scaleLabel` key. It defines options for the scale title. Note that this only applies to cartesian axes.
+
+| Name | Type | Default | Description
+| ---- | ---- | ------- | -----------
+| `display` | `boolean` | `false` | If true, display the axis title.
+| `labelString` | `string` | `''` | The text for the title. (i.e. "# of People" or "Response Choices").
+| `lineHeight` | <code>number&#124;string</code> | `1.2` | Height of an individual line of text (see [MDN](https://developer.mozilla.org/en-US/docs/Web/CSS/line-height)).
+| `fontColor` | `Color` | `'#666'` | Font color for scale title.
+| `fontFamily` | `string` | `"'Helvetica Neue', 'Helvetica', 'Arial', sans-serif"` | Font family for the scale title, follows CSS font-family options.
+| `fontSize` | `number` | `12` | Font size for scale title.
+| `fontStyle` | `string` | `'normal'` | Font style for the scale title, follows CSS font-style options (i.e. normal, italic, oblique, initial, inherit).
+| `padding` | <code>number&#124;object</code> | `4` | Padding to apply around scale labels. Only `top` and `bottom` are implemented.
+
+## Creating Custom Tick Formats
+
+It is also common to want to change the tick marks to include information about the data type. For example, adding a dollar sign ('$'). To do this, you need to override the `ticks.callback` method in the axis configuration.
+In the following example, every label of the Y axis would be displayed with a dollar sign at the front.
+
+If the callback returns `null` or `undefined` the associated grid line will be hidden.
+
+```javascript
+var chart = new Chart(ctx, {
+    type: 'line',
+    data: data,
+    options: {
+        scales: {
+            yAxes: [{
+                ticks: {
+                    // Include a dollar sign in the ticks
+                    callback: function(value, index, values) {
+                        return '$' + value;
+                    }
+                }
+            }]
+        }
+    }
+});
+```