util-array-object-or-both^4.0.1

import { strict as assert } from "assert";
import { arrObjOrBoth } from "util-array-object-or-both";

// normalises string, a user preference:

assert.equal(arrObjOrBoth("arrays"), "array");
assert.equal(arrObjOrBoth("array"), "array");
assert.equal(arrObjOrBoth("arr"), "array");
assert.equal(arrObjOrBoth("a"), "array");

assert.equal(arrObjOrBoth("objects"), "object");
assert.equal(arrObjOrBoth("object"), "object");
assert.equal(arrObjOrBoth("obj"), "object");
assert.equal(arrObjOrBoth("o"), "object");

assert.equal(arrObjOrBoth("whatever"), "any");
assert.equal(arrObjOrBoth("either"), "any");
assert.equal(arrObjOrBoth("both"), "any");
assert.equal(arrObjOrBoth("any"), "any");
assert.equal(arrObjOrBoth("all"), "any");
assert.equal(arrObjOrBoth("e"), "any");

`${opts.msg}The ${opts.optsVarName} was customised to an unrecognised value: ${str}. Please check it against the API documentation.`

`ast-delete-key/deleteKey(): [THROW_ID_01] The variable "opts.only" was customised to an unrecognised value: sweetcarrots. Please check it against the API documentation.`

// require this library:
const { arrObjOrBoth } = require('util-array-object-or-both')
// and friends:
const clone = require('lodash.clonedeep')
const checkTypes = require('check-types-mini')
const objectAssign = require('object-assign')
// let's say you have a function:
function myPrecious (input, opts) {
  // now you want to check your options object, is it still valid after users have laid their sticky paws on it:
  // define defaults:
  let defaults = {
    lalala: null,
    only: 'object' // <<< this is the value we're particularly keen to validate, is it `array`|`object`|`any`
  }
  // clone the defaults to safeguard it, and then, object-assign onto defaults.
  // basically you fill missing values with default-ones
  opts = objectAssign(clone(defaults), opts)
  // now, use "check-types-mini" to validate the types:
  checkTypes(opts, defaults,
    {
      // give a meaningful message in case it throws,
      // customise the library `check-types-mini`:
      msg: 'my-library/myPrecious(): [THROW_ID_01]',
      optsVarName: 'opts',
      schema: {
        lalala: ['null', 'string'],
        only: ['null', 'string']
      }
    }
  )
  // by this point, we can guarantee that opts.only is either `null` or `string`.
  // if it's a `string`, let's validate is its values among accepted-ones:
  opts.only = arrObjOrBoth(opts.only, {
    msg: 'my-library/myPrecious(): [THROW_ID_02]',
    optsVarName: 'opts.only'
  })
  // now we can guarantee that it's either falsy (undefined or null) OR:
  //   - `object`
  //   - `array`
  //   - `any`

  // now you can use `opts.only` in your function safely.
  ...
  // rest of the function...
}