babel-plugin-syntax-exists

Babel Plugin: syntax-exists

This is a Babel plugin which adds syntax for making existential checks in your code.
It uses the the keyword ex which is short for exists. :sparkles:

Features

• Return true if value exists
• Return false if value is null or undefined
• Return child if parent exists
• Return false on child if parent is null or undefined
• Return function call if value is a function
• Return false for function call if value is not a function

What?

From The Little Book on Coffeescript:

Using if for null checks in JavaScript is common, but has a few pitfalls in that empty strings and zero are both coerced into false, which can catch you out. CoffeeScript existential operator ? returns true unless a variable is null or undefined, similar to Ruby's nil?.

So what does it look like?

foo.ex compiles to typeof foo !== "undefined" && foo !== null

How about a more exhilirating use case?

Given an object:

let obj = {
  attr: 'value',
  nested_attr: { name: 'nested' },
  func: () => 777
}

We can write write the following statements and expect the subsequent returns:

obj.ex.attr              // 'value'
obj.attr.ex              // true
obj.nested_attr.ex.name  // 'nested'

// Oh, and it works for functions too...
// --------------------------------------
obj.func.ex              // true
obj.func.ex()            // 777

// But what about undefined errors?
// --------------------------------------
obj.doesnt_exist.ex      // false
// obj.doesnt_exist.ex.nope // false
obj.not_a_func.ex()      // false

Installation

$ npm install babel-plugin-syntax-exists

Usage

Via .babelrc (Recommended)

babelrc

{
  "plugins": ["syntax-exists"]
}

Via CLI

$ babel --plugins syntax-exists script.js

Via Node API

require('babel').transform('code',{
  plugins: ['syntax-exists']
});