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TypeScript - String Enum for Checking Value Type

Ramda's Type Check

Ramda's type checking returns a string, but in order for this to be useful, one needs to know if the returned value matches your intended assertion.

R.type({}); //=> "Object"
R.type(1); //=> "Number"
R.type(false); //=> "Boolean"
R.type('s'); //=> "String"
R.type(null); //=> "Null"
R.type([]); //=> "Array"
R.type(/[A-z]/); //=> "RegExp"
R.type(() => {}); //=> "Function"
R.type(undefined); //=> "Undefined"

Although there is a is function in Ramda that replicates the behavior of the example, the following will describe how a string enum will be used to replicate the is function (do use Ramda's built-in is function as it is more succinct).

The goal is to wrap Ramda's type check in a comparison function to perform the assertion for us. Create a string enum which will be used inside the function to check against Ramda's string return from the type check.

// typeCheck.ts

import { type as checkType } from 'ramda';

// String enum
export enum stringTypes {
  'Object',
  'Number',
  'Boolean',
  'String',
  'Null',
  'Array',
  'RegExp',
  'Function',
  'Undefined'
}

// checkType is R.type which returns a string to explain the checked value type that will be compared against the enum string
export function typeCheck(val: any, type: stringTypes): boolean {
  return checkType(val) === stringTypes[type];
}

Usage of the wrapped Ramda value type checking function.

import { typeCheck, stringTypes } from './type-check';

if (typeCheck(folderName, stringTypes.Undefined)) {
  // do something here
}