---
title: "Custom Functions"
enterprise: true
framework: javascript
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/javascript-data-grid/modules/). [Initial](https://www.ag-grid.com/javascript-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

```ts
import {
  ClientSideRowModelModule,
  FormulaFunctionParams,
  GetRowIdParams,
  GridApi,
  GridOptions,
  ModuleRegistry,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
  createGrid,
  enableDevValidations,
} from "ag-grid-community";
import { CellSelectionModule, FormulaModule } from "ag-grid-enterprise";

// Enable extended validations only for development
if (process.env.NODE_ENV !== "production") {
  enableDevValidations();
}

ModuleRegistry.registerModules([
  CellSelectionModule,
  ClientSideRowModelModule,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
  FormulaModule,
]);

let gridApi: GridApi;

const gridOptions: GridOptions = {
  columnDefs: [
    { field: "gold", colId: "c0" },
    { field: "silver", colId: "c1" },
    { field: "totals", colId: "c2", cellDataType: "text", allowFormula: true },
  ],
  getRowId: (params: GetRowIdParams) => String(params.data.rid),
  cellSelection: {
    handle: {
      mode: "fill",
    },
  },
  defaultColDef: {
    flex: 1,
    editable: true,
  },
  formulaFuncs: {
    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;
      },
    },
  },
  rowData: [
    { 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 gridDiv = document.querySelector<HTMLElement>("#myGrid")!;
gridApi = createGrid(gridDiv, gridOptions);
```

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

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

    // other grid options ...
}
```

## Error Handling

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

#### Custom Errors

```ts
import {
  ClientSideRowModelModule,
  FormulaFunctionParams,
  GetRowIdParams,
  GridApi,
  GridOptions,
  ModuleRegistry,
  TextEditorModule,
  TooltipModule,
  createGrid,
  enableDevValidations,
} from "ag-grid-community";
import { CellSelectionModule, FormulaModule } from "ag-grid-enterprise";

// Enable extended validations only for development
if (process.env.NODE_ENV !== "production") {
  enableDevValidations();
}

ModuleRegistry.registerModules([
  CellSelectionModule,
  ClientSideRowModelModule,
  FormulaModule,
  TextEditorModule,
  TooltipModule,
]);

let gridApi: GridApi;

const gridOptions: GridOptions = {
  columnDefs: [
    { 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" },
  ],
  getRowId: (params: GetRowIdParams) => String(params.data.rid),
  cellSelection: {
    handle: {
      mode: "fill",
    },
  },
  defaultColDef: {
    cellDataType: "text",
    allowFormula: true,
    editable: true,
    flex: 1,
  },
  formulaFuncs: {
    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.";
      },
    },
  },
  rowData: [
    { 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 gridDiv = document.querySelector<HTMLElement>("#myGrid")!;
gridApi = createGrid(gridDiv, gridOptions);
```

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

> **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

```ts
import {
  CellApiModule,
  ClientSideRowModelModule,
  FormulaFunctionParams,
  GetRowIdParams,
  GridApi,
  GridOptions,
  ModuleRegistry,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
  createGrid,
  enableDevValidations,
} from "ag-grid-community";
import { CellSelectionModule, FormulaModule } from "ag-grid-enterprise";

// Enable extended validations only for development
if (process.env.NODE_ENV !== "production") {
  enableDevValidations();
}

ModuleRegistry.registerModules([
  CellSelectionModule,
  ClientSideRowModelModule,
  FormulaModule,
  CellApiModule,
  NumberEditorModule,
  TextEditorModule,
  TooltipModule,
]);

let gridApi: GridApi;

const rowData = [
  { 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 gridOptions: GridOptions = {
  columnDefs: [
    { field: "gold", colId: "c0" },
    { field: "silver", colId: "c1" },
    { field: "result", colId: "c2", allowFormula: true },
  ],
  getRowId: (params: GetRowIdParams) => String(params.data.rid),
  cellSelection: {
    handle: {
      mode: "fill",
    },
  },
  defaultColDef: {
    editable: true,
    flex: 1,
  },
  rowData,
  formulaFuncs: {
    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;
      },
    },
  },
};

const gridDiv = document.querySelector<HTMLElement>("#myGrid")!;
gridApi = createGrid(gridDiv, gridOptions);
```

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

## 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/javascript-data-grid/formula-reference/) for built-in functions that can inspire custom implementations.