createFormData

The createFormData() function creates an extended FormData from nested values (objects and arrays) and keeps the original input in inputValues.

Supported values are:

• string, File, boolean, number, null, undefined
• DDate.TheDate, DDate.TheTime
• nested objects and arrays of these values

Use TheFormData.toFlatEntries(...) when you need explicit flattened key/value pairs, and TheFormData.fromEntries(...) to rebuild nested objects after receiving form-data entries on the backend. During flattening, non-File values are converted to strings (null becomes "null").

Interactive example

Syntax

type EligibleFormDataValue =
	| boolean
	| number
	| null
	| string
	| File
	| undefined
	| DDate.TheDate
	| DDate.TheTime
	| { [key: string]: EligibleFormDataValue }
	| EligibleFormDataValue[];

class TheFormData<
	GenericValues extends Record<string, EligibleFormDataValue>
> extends FormData {
	readonly inputValues: GenericValues;

	static toFlatEntries(
		value: EligibleFormDataValue,
		path?: string
	): Iterable<[string, string | File]>;

	static fromEntries(
		iterable: Iterable<[string, unknown]>,
		arrayMaxIndex: number
	): object;
}

function createFormData<
	GenericValues extends Record<string, EligibleFormDataValue>
>(
	inputValues: GenericValues
): TheFormData<GenericValues>;

Parameters

• inputValues : Nested input object to convert into FormData.
• iterable : Flat entries (typically FormData.entries() output) to reconstruct.
• arrayMaxIndex : Maximum accepted index when reconstructing arrays with fromEntries.
• value / path : Inputs used by toFlatEntries to recursively flatten data.

Return value

• createFormData(...) returns a TheFormData instance.
• TheFormData.toFlatEntries(...) returns an iterable of flat [path, value] pairs.
• TheFormData.fromEntries(...) returns a reconstructed nested object.

toFlatEntries(...) serializes boolean, number, null, DDate.TheDate, and DDate.TheTime as strings.

See also

• pipe - Compose transformations around createFormData
• stringToBytes - String parsing helper often used with multipart metadata