Dev's Toolbox // Typeguard

Utilities for checking the types of values at runtime, helpful for working with external or async loaded data within TypeScript.

API

createObjectTypeguard(shape)

Create a suite of typeguard functions for the given object shape.

• shape - The shape of the object to create a typeguard for.

Returns: DecoratedTypeguard

Shape

A TypeGuard Shape is an object whose keys specify how to analyze an objects types.

const guards = createObjectTypeguard({
  id: "number", // Strings imply "typeof" checks
  name: "string",
  active: "boolean",
  notes: {array: "string"}, // An array of strings
  metadata: {record: ["string", "number", "boolean"]} // A record whose values are strings, numbers or booleans
  website: {optional: "string"} // Optional value
  version: {literal: 1} // Literal value
});

DecoratedTypeguard

The return value of createObjectTypeguard is a function which can take an object and check if it matches the provided shape. This function also contains three additional guards as properties:

const isThing = createObjectTypeguard(THING_SHAPE);

isThing(value); // Check if `value` satisfies Thing
isThing.strict(value); // Check if `value` is exactly a Thing with no additional properties
isThing.array(value); // Check if `value` is an array of Things
isThing.strictArray(value); // Check if `value` is an array of strictly-checked Things

checkValue(value, checker)

Check a single non-object type.

• value - The value to check the type of
• checker - The type expression to check against

Returns: boolean

checkArray(value checker)

Check the type validity of the elements in an array.

• value - The value to check the type of
• checker - The type expression to check against

Returns: boolean

checkObject(value, shape)

Quickly check a single object shape.

• value - The value to test the type validity of
• shape - The shape the object should be, as a typeguard shape

Returns: boolean