> ## Documentation Index
> Fetch the complete documentation index at: https://fuse-docs.swovo.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Creating Column Types

> Defining your own column type in Fuse.

If the built-in column types are not enough, you can define your own data structure using the String column. You do this through the use of `onValidateRecord`. You simply need to validate that the value passed to `onValidateRecord` matches your desired format.

## Example of Creating a "Currency" Column

```javascript theme={null}
// matches formats like $10
const currencyRegex = /\$[0-9]*/;

const importer = new FuseImporter();

importer.getSessionToken = ... // see https://fuse-docs.flatirons.com/getting-started/sessions

importer.addColumn({
  internal_key: "total_charge",
  label: "Total Charge",
  column_type: "string",
  required: true,
  position: 1,
  unique: true,
});

importer.onValidateRecord = async (record) => {
  const errors = {};
  const warnings = {};

  // make sure the total charge matches the regex
  if (!record.total_charge?.match(currencyRegex)) {
    errors["total_charge"] =
      "Total charge must be a dollar amount matching the format $xx";
  }

  return {
    errors: errors,
    warnings: warnings,
  };
};

importer.show();
```