One of the main features of tydel is that it is strictly based on typed values.

A list of type expressions are already shipped with the package and you can import them as follows:

import { Types } from 'tydel';

Some of the types include:

  • Types.string
  • Types.number
  • Types.enum
  • …see API Reference for more.

Primary types

If you want to check the type of a value that you expect to be a string:

const checkIfString = Types.string;

Now the checkIfString function would return a string if a correct valid string was passed to it, otherwise it would throw a new TypeError.

const str = checkIfString('Hello World'); // returns `Hello World`

const foo = checkIfString([1, 2, 3]); // throws TypeError


Type expressions can also be chained:

const checkIfString = Types.string.isRequired;

checkIfString('hello world'); // returns `hello world`

checkIfString(); // throws TypeError: value is undefined

Available chained expressions:

  • isRequired
  • defaults(defaultValue)