---
title: "Custom Functions"
enterprise: true
framework: react
version: "36.1.0"
---

# Custom Functions

Custom formula functions let you extend the engine with domain-specific logic and reusable calculations.

## Formula Functions API

Custom functions are provided through the `formulaFuncs` grid option.

| Property | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| `formulaFuncs` | `FormulaFuncs` |  |  | A map of 'function name' to 'function' for custom functions that are used for formulas. Module: [`FormulaModule`](https://www.ag-grid.com/react-data-grid/modules/). [Initial](https://www.ag-grid.com/react-data-grid/grid-interface/#initial-grid-options). |

## Simple Example

The example below registers `CUSTOMSUM`, which iterates over all values passed to the function (including ranges) and returns their sum.

#### Simple Iterator

```tsx
"use client";

import React, {
  useCallback,
  useMemo,
  useRef,
  useState,
  StrictMode,
} from "react";
import { createRoot } from "react-dom/client";
import { AgGridReact, AgGridProvider } from "ag-grid-react";
import {
  CellSelectionOptions,
  ClientSideRowModelModule,
  ColDef,
  ColGroupDef,
  FormulaFuncs,
  FormulaFunctionParams,
  GetRowIdFunc,
  GetRowIdParams,
  GridApi,
  GridOptions,
  ModuleRegistry,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
  enableDevValidations,
} from "ag-grid-community";
import { CellSelectionModule, FormulaModule } from "ag-grid-enterprise";

if (process.env.NODE_ENV !== "production") {
  enableDevValidations();
}

const modules = [
  CellSelectionModule,
  ClientSideRowModelModule,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
  FormulaModule,
];

const GridExample = () => {
  const containerStyle = useMemo(() => ({ width: "100%", height: "100%" }), []);
  const gridStyle = useMemo(() => ({ height: "100%", width: "100%" }), []);
  const [rowData, setRowData] = useState<any[]>([
    { rid: "1", gold: 1, silver: 1, totals: "=CUSTOMSUM(A1:B1)" },
    { rid: "2", gold: 1, silver: 2, totals: "=CUSTOMSUM(A2:B2)" },
    { rid: "3", gold: 4, silver: 0, totals: "=CUSTOMSUM(A3:B3)" },
    { rid: "4", gold: 0, silver: 0, totals: "=CUSTOMSUM(A4:B4)" },
    { rid: "5", gold: 2, silver: 13, totals: "=CUSTOMSUM(A5:B5)" },
    { rid: "6", gold: 0, silver: 1, totals: "=CUSTOMSUM(A6:B6)" },
    { rid: "7", gold: 9, silver: 6, totals: "=CUSTOMSUM(A7:B7)" },
    { rid: "8", gold: 0, silver: 11, totals: "=CUSTOMSUM(A1:B8, B1)" },
  ]);
  const [columnDefs, setColumnDefs] = useState<ColDef[]>([
    { field: "gold", colId: "c0" },
    { field: "silver", colId: "c1" },
    { field: "totals", colId: "c2", cellDataType: "text", allowFormula: true },
  ]);
  const getRowId = useCallback(
    (params: GetRowIdParams) => String(params.data.rid),
    [],
  );
  const cellSelection = useMemo<boolean | CellSelectionOptions>(() => {
    return {
      handle: {
        mode: "fill",
      },
    };
  }, []);
  const defaultColDef = useMemo<ColDef>(() => {
    return {
      flex: 1,
      editable: true,
    };
  }, []);
  const formulaFuncs = useMemo<FormulaFuncs>(() => {
    return {
      CUSTOMSUM: {
        func: (params: FormulaFunctionParams) => {
          let total = 0;
          for (const value of params.values) {
            const num = Number(value);
            if (Number.isFinite(num)) {
              total += num;
            }
          }
          return total;
        },
      },
    };
  }, []);

  return (
    <AgGridProvider modules={modules}>
      <div style={containerStyle}>
        <div style={gridStyle}>
          <AgGridReact
            rowData={rowData}
            columnDefs={columnDefs}
            getRowId={getRowId}
            cellSelection={cellSelection}
            defaultColDef={defaultColDef}
            formulaFuncs={formulaFuncs}
          />
        </div>
      </div>
    </AgGridProvider>
  );
};

const root = createRoot(document.getElementById("root")!);
root.render(
  <StrictMode>
    <GridExample />
  </StrictMode>,
);
```

[Live example: Simple Iterator](https://www.ag-grid.com/examples/formula-custom-functions/formulas-simple-iterator/reactFunctionalTs)

```jsx
const [columnDefs, setColumnDefs] = useState([
    { field: 'sales' },
    { field: 'calculated', allowFormula: true },
]);
const formulaFuncs = {
    CUSTOMSUM: {
        func: (params) => {
            let total = 0;
            for (const value of params.values) {
                total += value;
            }
            return total;
        },
    },
};

<AgGridReact
    columnDefs={columnDefs}
    formulaFuncs={formulaFuncs}
/>
```

## Error Handling

Your function should throw when arguments are invalid. Errors are surfaced in the grid and propagate through dependent formulas.

#### Custom Errors

```tsx
"use client";

import React, {
  useCallback,
  useMemo,
  useRef,
  useState,
  StrictMode,
} from "react";
import { createRoot } from "react-dom/client";
import { AgGridReact, AgGridProvider } from "ag-grid-react";
import {
  CellSelectionOptions,
  ClientSideRowModelModule,
  ColDef,
  ColGroupDef,
  FormulaFuncs,
  FormulaFunctionParams,
  GetRowIdFunc,
  GetRowIdParams,
  GridApi,
  GridOptions,
  ModuleRegistry,
  TextEditorModule,
  TooltipModule,
  enableDevValidations,
} from "ag-grid-community";
import { CellSelectionModule, FormulaModule } from "ag-grid-enterprise";

if (process.env.NODE_ENV !== "production") {
  enableDevValidations();
}

const modules = [
  CellSelectionModule,
  ClientSideRowModelModule,
  FormulaModule,
  TextEditorModule,
  TooltipModule,
];

const GridExample = () => {
  const containerStyle = useMemo(() => ({ width: "100%", height: "100%" }), []);
  const gridStyle = useMemo(() => ({ height: "100%", width: "100%" }), []);
  const [rowData, setRowData] = useState<any[]>([
    { rid: 1, A: 1, B: 2, C: 3 },
    { rid: 2, A: 4, B: 5, C: 6 },
    { rid: 3, A: 2, B: 5, C: 2 },
    { rid: 4, A: 7, B: 8, C: 9 },
    { rid: 5, A: 0, B: 80, C: 10 },
    { rid: 6, A: 0, B: 4, C: 7 },
    { rid: 7, A: 7, B: 2, C: 2 },
    { rid: 8, A: 1, B: 0, C: 2 },
    {
      rid: 9,
      A: '=ERRORIFONE(REF(COLUMN("0"),ROW("1"),COLUMN("0"),ROW("8")))',
      B: '=ERRORIFONE(REF(COLUMN("1"),ROW("1"),COLUMN("1"),ROW("8")))',
      C: '=ERRORIFONE(REF(COLUMN("2"),ROW("1"),COLUMN("2"),ROW("8")))',
      D: '=CONCAT(REF(COLUMN("0"),ROW("9"),COLUMN("2"),ROW("9")))',
    },
  ]);
  const [columnDefs, setColumnDefs] = useState<ColDef[]>([
    { field: "A", colId: "0", headerName: "Gold" },
    { field: "B", colId: "1", headerName: "Silver" },
    { field: "C", colId: "2", headerName: "Bronze" },
    { field: "D", colId: "3", headerName: "Check Error Propagation" },
  ]);
  const getRowId = useCallback(
    (params: GetRowIdParams) => String(params.data.rid),
    [],
  );
  const cellSelection = useMemo<boolean | CellSelectionOptions>(() => {
    return {
      handle: {
        mode: "fill",
      },
    };
  }, []);
  const defaultColDef = useMemo<ColDef>(() => {
    return {
      cellDataType: "text",
      allowFormula: true,
      editable: true,
      flex: 1,
    };
  }, []);
  const formulaFuncs = useMemo<FormulaFuncs>(() => {
    return {
      ERRORIFONE: {
        func: (params: FormulaFunctionParams) => {
          for (const value of params.values) {
            if (String(value) === "1") {
              throw "Error, discovered a '1' in params";
            }
          }
          return "SUCCESS, no '1' found.";
        },
      },
    };
  }, []);

  return (
    <AgGridProvider modules={modules}>
      <div style={containerStyle}>
        <div style={gridStyle}>
          <AgGridReact
            rowData={rowData}
            columnDefs={columnDefs}
            getRowId={getRowId}
            cellSelection={cellSelection}
            defaultColDef={defaultColDef}
            formulaFuncs={formulaFuncs}
          />
        </div>
      </div>
    </AgGridProvider>
  );
};

const root = createRoot(document.getElementById("root")!);
root.render(
  <StrictMode>
    <GridExample />
  </StrictMode>,
);
```

[Live example: Custom Errors](https://www.ag-grid.com/examples/formula-custom-functions/formulas-custom-errors/reactFunctionalTs)

> **Note**
>
> When a function (or a referenced cell) throws an error, the cell displays `#ERROR!` and hovering over the cell displays the thrown error message. Errors also propagate to dependent formula cells.

## Complex Example

This example shows `COUNTEQ`, which receives a range and a value and counts matches. It uses `params.args` to validate argument types and handle ranges explicitly.

#### Contextual Iterator

```tsx
"use client";

import React, {
  useCallback,
  useMemo,
  useRef,
  useState,
  StrictMode,
} from "react";
import { createRoot } from "react-dom/client";
import { AgGridReact, AgGridProvider } from "ag-grid-react";
import {
  CellApiModule,
  CellSelectionOptions,
  ClientSideRowModelModule,
  ColDef,
  ColGroupDef,
  FormulaFuncs,
  FormulaFunctionParams,
  GetRowIdFunc,
  GetRowIdParams,
  GridApi,
  GridOptions,
  ModuleRegistry,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
  enableDevValidations,
} from "ag-grid-community";
import { CellSelectionModule, FormulaModule } from "ag-grid-enterprise";

if (process.env.NODE_ENV !== "production") {
  enableDevValidations();
}

const modules = [
  CellSelectionModule,
  ClientSideRowModelModule,
  FormulaModule,
  CellApiModule,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
];

const GridExample = () => {
  const containerStyle = useMemo(() => ({ width: "100%", height: "100%" }), []);
  const gridStyle = useMemo(() => ({ height: "100%", width: "100%" }), []);
  const [rowData, setRowData] = useState<any[]>([
    { rid: "r1", gold: 1, silver: 2 },
    { rid: "r2", gold: 2, silver: 2 },
    { rid: "r3", gold: 1, silver: 20 },
    { rid: "r4", gold: 3, silver: 2 },
    { rid: "r5", gold: 5, silver: 7 },
    { rid: "r6", gold: 2, silver: 2 },
    { rid: "r7", gold: 1, silver: 2 },
    {
      rid: "r8",
      gold: 1,
      silver: 2,
      result: "=COUNTEQ($A$1:$B$8,2)",
    },
  ]);
  const [columnDefs, setColumnDefs] = useState<ColDef[]>([
    { field: "gold", colId: "c0" },
    { field: "silver", colId: "c1" },
    { field: "result", colId: "c2", allowFormula: true },
  ]);
  const getRowId = useCallback(
    (params: GetRowIdParams) => String(params.data.rid),
    [],
  );
  const cellSelection = useMemo<boolean | CellSelectionOptions>(() => {
    return {
      handle: {
        mode: "fill",
      },
    };
  }, []);
  const defaultColDef = useMemo<ColDef>(() => {
    return {
      editable: true,
      flex: 1,
    };
  }, []);
  const formulaFuncs = useMemo<FormulaFuncs>(() => {
    return {
      COUNTEQ: {
        func: (params: FormulaFunctionParams) => {
          const argsArr = Array.from(params.args);
          if (argsArr.length != 2) {
            throw "COUNTEQ requires exactly 2 arguments";
          }
          const [range, criteria] = argsArr;
          if (range.kind !== "range") {
            throw "First argument to COUNTEQ must be a range";
          }
          if (criteria.kind !== "value" || typeof criteria.value === "object") {
            throw "Second argument to COUNTEQ must be a primitive value";
          }
          const isNumCriteria = typeof criteria.value === "number";
          let count = 0;
          for (const value of range) {
            const coercedValue = isNumCriteria ? Number(value) : value;
            if (coercedValue === criteria.value) {
              count++;
            }
          }
          return count;
        },
      },
    };
  }, []);

  return (
    <AgGridProvider modules={modules}>
      <div style={containerStyle}>
        <div style={gridStyle}>
          <AgGridReact
            rowData={rowData}
            columnDefs={columnDefs}
            getRowId={getRowId}
            cellSelection={cellSelection}
            defaultColDef={defaultColDef}
            formulaFuncs={formulaFuncs}
          />
        </div>
      </div>
    </AgGridProvider>
  );
};

const root = createRoot(document.getElementById("root")!);
root.render(
  <StrictMode>
    <GridExample />
  </StrictMode>,
);
```

[Live example: Contextual Iterator](https://www.ag-grid.com/examples/formula-custom-functions/formulas-context-iterator/reactFunctionalTs)

## Best Practices

- Validate argument counts and types early.
- Prefer iterators (`params.values`) for large ranges to avoid unnecessary allocations.
- Keep functions pure and fast to avoid performance issues on large grids.

See [Formula Reference](https://www.ag-grid.com/react-data-grid/formula-reference/) for built-in functions that can inspire custom implementations.