discriminate

The discriminate() method discriminates an object by the value of a property (type guard for unions).

Interactive example

Syntax

Classic signature

function discriminate<
	GenericInput extends object,
	GenericKey extends keyof GenericInput,
	GenericInput extends EligibleEqual
>(
	input: GenericInput,
	key: GenericKey,
	value: (MaybeArray<(GenericInput & Extract<GenericInput[GenericKey], EligibleEqual>)> | MaybeArray<Extract<GenericInput[GenericKey], EligibleEqual>>)
): input is Extract<GenericInput, {
	[Prop in GenericKey]: GenericInput;
}>

Curried signature

function discriminate<
	GenericInput extends object,
	GenericKey extends keyof GenericInput,
	GenericInput extends EligibleEqual
>(
	key: GenericKey,
	value: ...
): (input: GenericInput) => input is Extract<GenericInput, {
	[Prop in GenericKey]: GenericInput;
}>

Parameters

• input: The object to discriminate (often a union type).
• key: The key of the discriminant property.
• input: The expected value (or array of values) for discrimination.

Return value

A boolean that acts as a type guard to narrow the union type.

See also

• deepDiscriminate - Discriminates by a deep property
• hasKeys - Checks for the presence of keys