telvis/README.md

Typescript/Javascript safe-navigation operator, also known as Elvis operator

# Telvis
Typescript/Javascript safe navigation

# About

This library adds a `path` method to the `Object` prototype which allows you to safely get a nested property of an object.
This is comparable to the elvis operator `?.` (Swift, C#) or monadic options like `Option.flatMap` (Scala) or `Maybe.#>>` (Haskell)

`a.path("b").path("c").path("d")` will return `a.b.c.d` if `a`, `b` and `c` and not `null` or `undefined`, and otherwise will return `undefined`.
This can also be shortened to `a.path("b","c","d")`

Note: Requires Typescript 2.1 because it uses the `keyof` operator

# Installation

`npm install telvis --save`

In your files: (**WIP**)
Sorry, still working out the modules

# Examples

```
interface A { b ?: B }
interface B { c ?: C }
interface C { hello ?: string }

let a1: A = { b : { hello: "world" }}
let a2: A = { b : {} }

// world will be of type string | undefined and at runtime will contain "world"
let world = a1.path("b", "hello")
// noworld will be of type string | undefined and at runtime will contain undefined
let noworld = a2.path("b", "hello")
// This will not compile, as "nonexistent" is not a key in A
// let invalid = a1.path("nonexistent") 
```