I wanted to implement Sanctuary's gets function to safely access a nested path on an object, but using Folktale 1.0's functions.
This implementation relies on Folktale's core.operators.get function. Though it returns a Maybe instead of value | undefined.
The gets method is particular handy for AWS Lambda functions, where the passed event is often a deeply-nested object.
| // Folktale dependencies | |
| const O = require('core.operators'); | |
| const Maybe = require('data.maybe'); | |
| // gets([keys], object) | |
| // [Strings] → Object → Just(α) | Nothing | |
| // | |
| // Takes an array of property names, and an object, and returns Just | |
| // the value at the given path if such a path exists, Nothing otherwise. | |
| // | |
| // Similar to Sanctuary's `gets` without the predicate: | |
| // https://sanctuary.js.org/#gets | |
| const gets = (keys) => (data) => | |
| keys.reduce( | |
| (acc, key) => acc.map(O.get(key)).chain(Maybe.fromNullable), | |
| Maybe.of(data) | |
| ) | |
| const data = { foo: { bar: {baz: 1}}} | |
| console.log(gets(['foo', 'bar', 'baz'])(data)) | |
| // => Just(1) | |
| console.log(gets(['foo', 'missingkey'])(data)) | |
| // => Nothing |