Typescript Docs Javascript Equality

One thing to be careful about in JavaScript is the difference between == and ===. As JavaScript tries to be resilient against programming errors == tries to do type coercion between two variables e.g. converts a string to a number so that you can compare with a number as shown below:

console.log(5 == "5"); // true   , TS Error
console.log(5 === "5"); // false , TS Error

So, anytime you have multiple async operations to coordinate in some way, I immediately want to go to promises. And, the best way to use promises to coordinate a number of async operations is to make each async operation return a promise. The lowest level async operation you show is fs.readFile(). Since I use the Bluebird promise library, it has a function for "promisifying" a whole module's worth of async functions.

var Promise = require('bluebird');
var fs = Promise.promisifyAll(require('fs'));

https://ponyfoo.com/articles/es6-modules-in-depth

In case it isn’t immediately obvious – you should 'use strict' in all the places. Even though it’s becoming de-facto in ES6, it’s still a good practice to use 'use strict' everywhere in ES6.

In the ES6 module system, strict mode is turned on by default. In case you don’t know what strict mode is, it’s just a stricter version of the language that disallows lots of bad parts of the language. It enables compilers to perform better by disallowing non-sensical behavior in user code, too.

The following is a summary extracted from changes documented in the strict mode article on MDN.

• Variables can’t be left undeclared