eslinq v0.1.0

ESLinq

An elegant way of working with iterables

ESLinq aims to be a complete, robust, thoroughly tested port of Linq to Objects to ECMAScript 2015 (ES6).

API Documentation

A first example

Problem: We have an array of users. A user can have multiple email addresses, and not all users are verified. We need a list of the email addresses of the verified users, and check if all of them end in ".com".

const users = [
	{
		"id": 12,
		"name": "John Smith",
		"emails": ["john.smith@example.com", "jsmith@live.com", "j.s967@gmail.com"],
		"verified": true
	},
	{
		"id": 56,
		"name": "Jennifer Brown",
		"emails": ["jbrown@gmail.com", "jennifer.brown@live.com"],
		"verified": false
	},
	{
		"id": 98,
		"name": "Kate Newton",
		"emails": ["katie6543@yahoo.com", "kate.newton.328@gmail.com"],
		"verified": true
	}
];

First, we need to restrict the list to only contain verified users:

const verifiedUsers = from(users).where(user => user.verified);

Then, we need to get a concatenated list of the email addresses of verified users:

const verifiedUserEmails =
    from(users)
	    .where(user => user.verified)
		.selectMany(user => user.emails);

It is important to note that verifiedUserEmails is a lazily evaluated iterable: filtering and transformation is only done once we start iterating it, e. g. with a for..of loop:

for (let email of verifiedUserEmails) {
	// The first time this loop executes is the first time the original iterable is read from.
	// Filtering (`where`) and transformation (`selectMany`) run element-by-element during iteration. 
	console.log(email);
}

Now let's check if all emails end with ".com":

const allEmailsEndWithCom =
    from(users)
	    .where(user => user.verified)
		.selectMany(user => user.emails)
		.all(email => email.endsWith(".com"));

The result is a bool value indicating whether all emails end with the substring ".com". The all operator is an eager one: it iterates through all elements to compute its value.