equal

The equal() function compares a value to one or several literals. With primitives, it acts as a type guard and restricts the type to the provided values.

Interactive example

Syntax

type EligibleEqual = string | null | number | undefined | bigint | boolean | symbol;

type ExpectLiteral<
	GenericInput extends EligibleEqual
> = Or<
	[
		UnionContain<GenericInput, string>,
		UnionContain<GenericInput, number>,
		UnionContain<GenericInput, boolean>,
		UnionContain<GenericInput, bigint>,
		UnionContain<GenericInput, symbol>
	]
> extends true ? never : GenericInput;

Classic signatures

// Type Guard predicate
function equal<
	GenericInput extends EligibleEqual | object,
	GenericInput extends Exclude<GenericInput, object>
>(
	input: GenericInput,
	value: ExpectLiteral<GenericInput> | ExpectLiteral<GenericInput>[]
): input is GenericInput;

// Boolean predicate
function equal<
	GenericInput extends EligibleEqual | object,
	GenericInput extends Exclude<GenericInput, object>
>(
	input: GenericInput,
	input: GenericInput | GenericInput[]
): boolean;

Curried signatures

// Type guard
function equal<
	GenericInput extends EligibleEqual | object,
	GenericInput extends Exclude<GenericInput, object>
>(
	value: ExpectLiteral<GenericInput> | ExpectLiteral<GenericInput>[]
): (input: GenericInput) => input is NoInfer<GenericInput>;

// Boolean predicate
function equal<
	GenericInput extends EligibleEqual | object,
	GenericInput extends Exclude<GenericInput, object>
>(
	input: GenericInput | GenericInput[]
): (input: GenericInput) => boolean;

Parameters

• input : Literal or array of allowed literals.
• input (direct overload) : Value to compare.

Return value

A boolean (or a type guard for primitives) indicating whether the input matches one of the values.

See also

• isType - Generic type guard based on runtime type
• instanceOf - Checks an instance of a constructor