check-types-mini

Check the types of your options object's values after user has customised them

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Table of Contents

• Install
• Idea
• API
  • Options object
  • For example
  • opts.enforceStrictKeyset
  • opts.schema
• Contributing
• Licence

Install

$ npm i -S check-types-mini

Idea

Imagine you have a library where you let users set the options object which comes as one of the input arguments.

Here's a challenge: how do you check (and throw) errors, easily, when users set your options to wrong things?

Answer: this library. It does all the work validating the inputs, lets you customise the throw error messages (like below) and even lets you provide the schema, that is, array of allowed types that each options key's value should be in.

For example, here's a typical throw error generated by this library:

TypeError: fancyLibrary/fancyFunction(): [THROW_ID_01] opts.placeholder was customised to "false" which is not boolean but string

Originally this library started as a function within one of my libraries. When I was about to copy-paste the thing into another library, I stopped and put that into a separate library, this library. I'm glad I did it, because already 7 of my libraries depend on it, and improving check-types I improve my other libraries. DRY at its best.

The point of check-types-mini is to save your time creating new libraries. Every library that has options object will need some type checks if you let user tinker with it.

API

checkTypes(obj[, ref, opts])

As a result, it throws TypeErrors for you, containing your custom message which you optionally set via arguments:

^ref can be null or undefined if all keys are set via opts.schema (see below).

Options object

For example

The common pattern is,

1. a) Define defaults object. Later it will be used to validate user's options, PLUS, if that's not enough, you can allow users to provide arrays of the matching type (set opts.acceptArrays to true)
2. b) Alternatively, you can skip defaults object and provide schema for each key via opts.schema. Just stick an object there, as a value, with all keys. Put allowed types in an array.
3. Object.assign cloned defaults onto the options object that comes from the input.
4. call check-types-mini with the above.
5. If input types mismatch, error will be thrown.

const checkTypes = require('check-types-mini')

function yourFunction (input, opts) {
  // declare defaults, so we can enforce types later:
  let defaults = {
    placeholder: false
  }
  // fill any settings with defaults if missing:
  opts = Object.assign({}, defaults, opts)

  // the check:
  checkTypes(opts, defaults, {msg: 'newLibrary/yourFunction(): [THROW_ID_01]', optsVarName: 'opts'})
  // ...
}

let res = yourFunction(1, {placeholder: 'zzz'})

// =>> [TypeError: 'newLibrary/yourFunction(): [THROW_ID_01] opts.placeholder was customised to "zzz" which is not boolean but string']

Sometimes you want to accept either a string (or type "X") or an arrays of strings (elements of type "X"). As long as ALL the elements within the array match the reference type, it's OK. For these cases set opts.acceptArrays to true.

This will throw:

const checkTypes = require('check-types-mini')
checkTypes(
  { // < input
    option1: 'setting1',
    option2: [true, true],
    option3: false
  },
  { // < reference
    option1: 'setting1',
    option2: false,
    option3: false
  }
)
// => Throws, because reference's `option2` is Boolean ("false") but input `option2` is array ("[true, true]").

But when we allow arrays of the matching type, it won't throw anymore:

const checkTypes = require('check-types-mini')
checkTypes(
  {
    option1: 'setting1',
    option2: ['setting3', 'setting4'],
    option3: false
  },
  {
    option1: 'setting1',
    option2: 'setting2',
    option3: false
  },
  {
    acceptArrays: true
  }
)
// => Does not throw, because we allow arrays full of a matching type

If you want, you can blacklist certain keys of your objects so that opts.acceptArrays will not apply to them. Just add keys into opts.acceptArraysIgnore array.

opts.enforceStrictKeyset

When I was coding a new major version of posthtml-ast-delete-object I had to update all the unit tests too. Previously, the settings were set using only one argument, Boolean-type. I had to change it to be a plain object. I noticed that when I missed updating some tests, their Booleans were Object.assigned into a default settings object and no alarm was being raised! That's not good.

Then I came up with the idea to enforce the keys of the object to match the reference and/or schema keys in options. It's on by default because I can't imagine how you would end up with settings object that does not match your default settings object, key-wise, but if you don't like that, feel free to turn it off. It's opts.enforceStrictKeyset Boolean flag.

opts.schema

Sometimes your API is more complex than a single type or array of them. Sometimes you want to allow, let's say, string or array of strings or null. What do you do?

Enter opts.schema. You can define all the types for particular key, as an array:

const checkTypes = require('check-types-mini')
checkTypes(
  {
    option1: 'setting1',
    option2: null
  },
  {
    option1: 'zz',
    option2: 'yy' // << notice, it's given as string in defaults object
  },
  {
    schema: {
      option2: ['stRing', null]
    }
  }
)
// => does not throw

The types are case-insensitive and come from type-detect, a Chai library:

• object (meaning a plain object literal, nothing else)
• array
• string
• null
• and other usual types

The type values you put into opts.schema are not validated, on purpose, so please don't make typos.

Contributing

All contributions are welcome. Please stick to Standard JavaScript notation and supplement the test.js with new unit tests covering your feature(s).

If you see anything incorrect whatsoever, do raise an issue. If you file a pull request, I'll do my best to help you to get it merged as soon as possible. If you have some advice how to improve this code, email me, I would really appreciate that.

Licence

MIT License (MIT)

Copyright (c) 2017 Codsen Ltd, Roy Revelt

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.