feat(react-charts): allow a function for cartesian tickFormat

change/@fluentui-react-charts-function-tickformat.json

@@ -0,0 +1,7 @@
+{
+  "type": "minor",
+  "comment": "feat: allow a function for the cartesian tickFormat so the numeric value axis can render a literal % or route through an app/i18n formatter (string behavior unchanged)",
+  "packageName": "@fluentui/react-charts",
+  "email": "michael@xerilium.com",
+  "dependentChangeType": "patch"
+}

packages/charts/react-charts/library/etc/react-charts.api.md

@@ -237,7 +237,7 @@ export interface CartesianChartProps {
     strokeWidth?: number;
     styles?: CartesianChartStyles;
     svgProps?: React_2.SVGProps<SVGSVGElement>;
-    tickFormat?: string;
+    tickFormat?: string | ((value: number | Date) => string);
     tickPadding?: number;
     tickValues?: number[] | Date[] | string[] | undefined;
     timeFormatLocale?: TimeLocaleDefinition;
@@ -1496,7 +1496,7 @@ export interface ModifiedCartesianChartProps extends CartesianChartProps {
     stringDatasetForYAxisDomain?: string[];
     tickParams?: {
         tickValues?: number[] | Date[] | string[];
-        tickFormat?: string;
+        tickFormat?: string | ((value: number | Date) => string);
     };
     xAxisInnerPadding?: number;
     xAxisOuterPadding?: number;

packages/charts/react-charts/library/src/components/CommonComponents/CartesianChart.types.ts

@@ -239,11 +239,16 @@ export interface CartesianChartProps {
   tickValues?: number[] | Date[] | string[] | undefined;
 
   /**
-   * the format for the data on x-axis. For date object this can be specified to your requirement. Eg: '%m/%d', '%d'
-   * Please look at https://github.com/d3/d3-time-format for all the formats supported for date axis
-   * Only applicable for date axis. For y-axis format use yAxisTickFormat prop.
+   * Format for x-axis tick labels. Accepts either a d3-format string or a `(value) => string` function.
+   *
+   * String: a d3-time-format specifier for date axes (e.g. `'%m/%d'`) or a d3-format specifier for
+   * numeric axes. See https://github.com/d3/d3-time-format and https://github.com/d3/d3-format.
+   *
+   * Function: formats the tick value directly — useful when a d3-format string is insufficient,
+   * e.g. appending a literal `%` to an already-0–100 axis (d3's `%` type multiplies by 100),
+   * or routing ticks through an app/i18n formatter. For y-axis format use `yAxisTickFormat`.
    */
-  tickFormat?: string;
+  tickFormat?: string | ((value: number | Date) => string);
 
   /**
    * Width of line stroke
@@ -644,7 +649,7 @@ export interface ModifiedCartesianChartProps extends CartesianChartProps {
    */
   tickParams?: {
     tickValues?: number[] | Date[] | string[];
-    tickFormat?: string;
+    tickFormat?: string | ((value: number | Date) => string);
   };
 
   /**

packages/charts/react-charts/library/src/utilities/UtilityUnitTests.test.ts

@@ -212,6 +212,16 @@ describe('createNumericXAxis', () => {
     utils.createNumericXAxis(xAxisParams, {}, utils.ChartTypes.HorizontalBarChartWithAxis);
     expect(xAxisParams.xAxisElement).toMatchSnapshot();
   });
+
+  it('should format value-axis ticks with a function tickFormat (e.g. a literal %)', () => {
+    const xAxisParams = createXAxisParams();
+    const result = utils.createNumericXAxis(
+      xAxisParams,
+      { tickFormat: (value: number | Date) => `${value as number}%` },
+      utils.ChartTypes.HorizontalBarChartWithAxis,
+    );
+    expect(result.tickLabels.every((label: string) => label.endsWith('%'))).toBe(true);
+  });
 });
 
 conditionalDescribe(isTimezoneSet(Timezone.UTC) && env === 'TEST')('createDateXAxis', () => {
@@ -274,6 +284,14 @@ conditionalDescribe(isTimezoneSet(Timezone.UTC) && env === 'TEST')('createDateXA
     });
     expect(xAxisParams.xAxisElement).toMatchSnapshot();
   });
+
+  it('should format date-axis ticks with a function tickFormat', () => {
+    const xAxisParams = createXAxisParams({ domainNRangeValues });
+    const result = utils.createDateXAxis(xAxisParams, {
+      tickFormat: (value: number | Date) => `Y${(value as Date).getFullYear()}`,
+    });
+    expect(result.tickLabels.every((label: string) => label.startsWith('Y'))).toBe(true);
+  });
 });
 
 describe('createStringXAxis', () => {

packages/charts/react-charts/library/src/utilities/utilities.ts

@@ -188,7 +188,7 @@ export interface IXAxisParams extends AxisProps {
 }
 export interface ITickParams {
   tickValues?: Date[] | number[] | string[];
-  tickFormat?: string;
+  tickFormat?: string | ((value: number | Date) => string);
 }
 
 export interface IYAxisParams extends AxisProps {
@@ -288,7 +288,9 @@ export function createNumericXAxis(
       return tickText[_index];
     }
     if (tickParams.tickFormat) {
-      return d3Format(tickParams.tickFormat)(domainValue);
+      return typeof tickParams.tickFormat === 'function'
+        ? tickParams.tickFormat(domainValue)
+        : d3Format(tickParams.tickFormat)(domainValue);
     }
     const xAxisValue = typeof domainValue === 'number' ? domainValue : domainValue.valueOf();
     return defaultFormat?.(xAxisValue) === '' ? '' : (formatToLocaleString(xAxisValue, culture) as string);
@@ -504,6 +506,9 @@ export function createDateXAxis(
     if (timeFormatLocale) {
       return formatFn(domainValue);
     }
+    if (typeof tickParams.tickFormat === 'function') {
+      return tickParams.tickFormat(domainValue);
+    }
     if (culture === undefined && tickParams.tickFormat) {
       if (useUTC) {
         return d3UtcFormat(tickParams.tickFormat)(domainValue);

packages/charts/react-charts/stories/src/HorizontalBarChartWithAxis/HorizontalBarChartWithAxisFunctionTickFormat.stories.tsx

@@ -0,0 +1,35 @@
+import * as React from 'react';
+import type { JSXElement } from '@fluentui/react-components';
+import type { HorizontalBarChartWithAxisDataPoint } from '@fluentui/react-charts';
+import { HorizontalBarChartWithAxis, getColorFromToken, DataVizPalette } from '@fluentui/react-charts';
+
+export const HorizontalBarWithAxisFunctionTickFormat = (): JSXElement => {
+  const points: HorizontalBarChartWithAxisDataPoint[] = [
+    { x: 10, y: 'Q1', legend: 'Completion', color: getColorFromToken(DataVizPalette.color1) },
+    { x: 45, y: 'Q2', legend: 'Completion', color: getColorFromToken(DataVizPalette.color2) },
+    { x: 72, y: 'Q3', legend: 'Completion', color: getColorFromToken(DataVizPalette.color3) },
+    { x: 95, y: 'Q4', legend: 'Completion', color: getColorFromToken(DataVizPalette.color4) },
+  ];
+
+  return (
+    <div style={{ width: '500px', height: '250px' }}>
+      <HorizontalBarChartWithAxis
+        chartTitle="Function tickFormat — literal % on a 0–100 axis"
+        data={points}
+        width={500}
+        height={250}
+        tickFormat={(value: number | Date) => `${value as number}%`}
+      />
+    </div>
+  );
+};
+
+HorizontalBarWithAxisFunctionTickFormat.parameters = {
+  docs: {
+    description: {
+      story:
+        'Demonstrates passing a function to `tickFormat`. A d3-format `%` string would multiply the value by 100, ' +
+        'double-scaling an already-0–100 axis. A function formats the tick directly, appending a literal `%`.',
+    },
+  },
+};

packages/charts/react-charts/stories/src/HorizontalBarChartWithAxis/index.stories.tsx

@@ -8,6 +8,7 @@ export { HorizontalBarWithAxisStringAxisTooltip } from './HorizontalBarChartWith
 export { HorizontalBarWithAxisDynamic } from './HorizontalBarChartWithAxisDynamic.stories';
 export { HorizontalBarWithAxisNegative } from './HorizontalBarChartWithAxisNegative.stories';
 export { HorizontalBarWithAxisCategoryOrder } from './HorizontalBarChartWithAxisCategoryOrder.stories';
+export { HorizontalBarWithAxisFunctionTickFormat } from './HorizontalBarChartWithAxisFunctionTickFormat.stories';
 
 export default {
   title: 'Charts/HorizontalBarChartWithAxis',