The in operator, when used with arrays in JavaScript, comes with a little nuance and may be the cause of some confusion. The in operator is strictly used to tell whether a given property name exists in an object or its [[Prototype]] chain (and is enumerable, but we’ll cover that later). So how does this work for arrays? It’s tempting to think 2 is in [1, 2] but this will return false.

I recently discovered the new customElements API and, after some experimentation, I decided to write about its awesomeness. The Custom Elements API allows web developers to define their own top-level HTML elements, thus promoting reusability among the Web Components community. On top of creating your own elements, you can extend the functionality of existing elements and share your elements with other developers.

This article is intended to further your knowledge of the various phases a DOM event goes through.

Consider the following problem statements:

Given the heads to two sorted linked lists, return a pointer to the head of a linked list containing all elements in both lists in sorted order.