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# figgy-pudding [](https://npm.im/figgy-pudding) [](https://npm.im/figgy-pudding) [](https://travis-ci.org/zkat/figgy-pudding) [](https://ci.appveyor.com/project/zkat/figgy-pudding) [](https://coveralls.io/github/zkat/figgy-pudding?branch=latest)
[`figgy-pudding`](https://github.com/zkat/figgy-pudding) is a small JavaScript
library for managing and composing cascading options objects -- hiding what
needs to be hidden from each layer, without having to do a lot of manual munging
and passing of options.
### The God Object is Dead!
### Now Bring Us Some Figgy Pudding!
## Install
`$ npm install figgy-pudding`
## Table of Contents
* [Example](#example)
* [Features](#features)
* [API](#api)
* [`figgyPudding(spec)`](#figgy-pudding)
* [`PuddingFactory(values)`](#pudding-factory)
* [`opts.get()`](#opts-get)
* [`opts.concat()`](#opts-concat)
* [`opts.toJSON()`](#opts-to-json)
* [`opts.forEach()`](#opts-for-each)
* [`opts[Symbol.iterator]()`](#opts-symbol-iterator)
* [`opts.entries()`](#opts-entries)
* [`opts.keys()`](#opts-keys)
* [`opts.value()`](#opts-values)
### Example
```javascript
// print-package.js
const fetch = require('./fetch.js')
const puddin = require('figgy-pudding')
const PrintOpts = puddin({
json: { default: false }
})
async function printPkg (name, opts) {
// Expected pattern is to call this in every interface function. If `opts` is
// not passed in, it will automatically create an (empty) object for it.
opts = PrintOpts(opts)
const uri = `https://registry.npmjs.com/${name}`
const res = await fetch(uri, opts.concat({
// Add or override any passed-in configs and pass them down.
log: customLogger
}))
// The following would throw an error, because it's not in PrintOpts:
// console.log(opts.log)
if (opts.json) {
return res.json()
} else {
return res.text()
}
}
console.log(await printPkg('figgy', {
// Pass in *all* configs at the toplevel, as a regular object.
json: true,
cache: './tmp-cache'
}))
```
```javascript
// fetch.js
const puddin = require('figgy-pudding')
const FetchOpts = puddin({
log: { default: require('npmlog') },
cache: {}
})
module.exports = async function (..., opts) {
opts = FetchOpts(opts)
}
```
### Features
* hide options from layer that didn't ask for it
* shared multi-layer options
* make sure `opts` argument is available
* transparent key access like normal keys, through a Proxy. No need for`.get()`!
* default values
* key aliases
* arbitrary key filter functions
* key/value iteration
* serialization
* 100% test coverage using `tap --100`
### API
#### <a name="figgy-pudding"></a> `> figgyPudding({ key: { default: val } | String }, [opts]) -> PuddingFactory`
Defines an Options constructor that can be used to collect only the needed
options.
An optional `default` property for specs can be used to specify default values
if nothing was passed in.
If the value for a spec is a string, it will be treated as an alias to that
other key.
##### Example
```javascript
const MyAppOpts = figgyPudding({
lg: 'log',
log: {
default: () => require('npmlog')
},
cache: {}
})
```
#### <a name="pudding-factory"></a> `> PuddingFactory(...providers) -> FiggyPudding{}`
Instantiates an options object defined by `figgyPudding()`, which uses
`providers`, in order, to find requested properties.
Each provider can be either a plain object, a `Map`-like object (that is, one
with a `.get()` method) or another figgyPudding `Opts` object.
When nesting `Opts` objects, their properties will not become available to the
new object, but any further nested `Opts` that reference that property _will_ be
able to read from their grandparent, as long as they define that key. Default
values for nested `Opts` parents will be used, if found.
##### Example
```javascript
const ReqOpts = figgyPudding({
follow: {}
})
const opts = ReqOpts({
follow: true,
log: require('npmlog')
})
opts.follow // => true
opts.log // => Error: ReqOpts does not define `log`
const MoreOpts = figgyPudding({
log: {}
})
MoreOpts(opts).log // => npmlog object (passed in from original plain obj)
MoreOpts(opts).follow // => Error: MoreOpts does not define `follow`
```
#### <a name="opts-get"></a> `> opts.get(key) -> Value`
Gets a value from the options object.
##### Example
```js
const opts = MyOpts(config)
opts.get('foo') // value of `foo`
opts.foo // Proxy-based access through `.get()`
```
#### <a name="opts-concat"></a> `> opts.concat(...moreProviders) -> FiggyPudding{}`
Creates a new opts object of the same type as `opts` with additional providers.
Providers further to the right shadow providers to the left, with properties in
the original `opts` being shadows by the new providers.
##### Example
```js
const opts = MyOpts({x: 1})
opts.get('x') // 1
opts.concat({x: 2}).get('x') // 2
opts.get('x') // 1 (original opts object left intact)
```
#### <a name="opts-to-json"></a> `> opts.toJSON() -> Value`
Converts `opts` to a plain, JSON-stringifiable JavaScript value. Used internally
by JavaScript to get `JSON.stringify()` working.
Only keys that are readable by the current pudding type will be serialized.
##### Example
```js
const opts = MyOpts({x: 1})
opts.toJSON() // {x: 1}
JSON.stringify(opts) // '{"x":1}'
```
#### <a name="opts-for-each"></a> `> opts.forEach((value, key, opts) => {}, thisArg) -> undefined`
Iterates over the values of `opts`, limited to the keys readable by the current
pudding type. `thisArg` will be used to set the `this` argument when calling the
`fn`.
##### Example
```js
const opts = MyOpts({x: 1, y: 2})
opts.forEach((value, key) => console.log(key, '=', value))
```
#### <a name="opts-entries"></a> `> opts.entries() -> Iterator<[[key, value], ...]>`
Returns an iterator that iterates over the keys and values in `opts`, limited to
the keys readable by the current pudding type. Each iteration returns an array
of `[key, value]`.
##### Example
```js
const opts = MyOpts({x: 1, y: 2})
[...opts({x: 1, y: 2}).entries()] // [['x', 1], ['y', 2]]
```
#### <a name="opts-symbol-iterator"></a> `> opts[Symbol.iterator]() -> Iterator<[[key, value], ...]>`
Returns an iterator that iterates over the keys and values in `opts`, limited to
the keys readable by the current pudding type. Each iteration returns an array
of `[key, value]`. Makes puddings work natively with JS iteration mechanisms.
##### Example
```js
const opts = MyOpts({x: 1, y: 2})
[...opts({x: 1, y: 2})] // [['x', 1], ['y', 2]]
for (let [key, value] of opts({x: 1, y: 2})) {
console.log(key, '=', value)
}
```
#### <a name="opts-keys"></a> `> opts.keys() -> Iterator<[key, ...]>`
Returns an iterator that iterates over the keys in `opts`, limited to the keys
readable by the current pudding type.
##### Example
```js
const opts = MyOpts({x: 1, y: 2})
[...opts({x: 1, y: 2}).keys()] // ['x', 'y']
```
#### <a name="opts-values"></a> `> opts.values() -> Iterator<[value, ...]>`
Returns an iterator that iterates over the values in `opts`, limited to the keys
readable by the current pudding type.
##### Example
'
```js
const opts = MyOpts({x: 1, y: 2})
[...opts({x: 1, y: 2}).values()] // [1, 2]
```