[I] FunctionValue

A function (fn) declared in the TypeSpec program.

By default, function values have very restrictive types, where the parameters have type never, and the return type is unknown.

To call a function, you must assert the type of the parameters. For example, if you have a FunctionValue that represents the following TypeSpec function:

extern fn example(a: valueof string, b: valueof int32): valueof boolean;

You can assert the parameter types in TypeScript like this:

const exampleFn: FunctionValue = ...; // however you obtain a reference to the function value, it will be strictly typed.

const assertedExampleFn = exampleFn as FunctionValue<[a: string, b: number], boolean>;

// Now you can call assertedExampleFn with the correct types:
ctx.callFunction(assertedExampleFn.implementation, "hello", 10);

Extends

• BaseValue

Type Parameters

Type Parameter	Default type
Parameters extends unknown[]	never[]
ReturnType	unknown

Properties

Property	Modifier	Type	Description	Overrides	Inherited from
entityKind	readonly	"Value"	-	-	BaseValue.entityKind
implementation	public	(ctx, …args) => ReturnType	The JavaScript implementation of the function. WARNING: Calling the implementation function directly is dangerous. It assumes that you have marshaled the arguments to JS values correctly and that you will handle the return value appropriately. Constructing the correct context is your responsibility (use the call methods of FunctionContext or DecoratorContext to create the context for you).	-	-
name?	public	string	The function’s name as declared in the TypeSpec source, if any.	-	-
namespace?	public	Namespace	The namespace in which this function was declared, if any.	-	-
node?	public	FunctionDeclarationStatementNode	-	-	-
parameters	public	MixedFunctionParameter[]	The parameters of the function.	-	-
returnType	public	MixedParameterConstraint	The return type constraint of the function.	-	-
type	public	Type	Represent the storage type of a value. Example `const a = “hello”; // Type here would be “hello” const b: string = a; // Type here would be string const c: string	int32 = b; // Type here would be string	int32`
valueKind	public	"Function"	-	BaseValue.valueKind	-