GraphQL operations are broken up into 2 types: queries and mutations. Queries are read-only, mutations modify data. Here's what you need to know about mutations in Apollo.

Apollo is a GraphQL server - it parses your GraphQL schema and provides a framework for you to define resolvers and mutations. Here's what you need to know.

The `v-for` directive lets you render a separate item for each element in an array. Here's what you need to know.

Unit testing is tricky, especially on the frontend. Here's a couple of patterns we use at Mastering JS for testing Vue components in isolation.

Vue instances have a `$refs` property that lets you access a Vue instance's child components. Here's what you need to know.

Puppeteer is a great tool for testing JavaScript apps in a real browser. Here's what you need to know.

State machines may seem like a dull abstract topic, but they are extremely useful for JavaScript developers. Here's what you need to know.

Async/await lets you write async code in a way that looks sync. No callbacks or promise chains, just `for` loops and `if` statements. Here's what you need to know.

When you call `new Promise` in JavaScript, you invoke the Promise constructor. Here's how you can use the Promise constructor like a pro.

Resolving a promise in JavaScript is how you mark a promise as fulfilled. Here's what you need to know.

The `Promise.all()` function lets you execute multiple promises in parallel, and accumulates the results. Here's what you need to know.

A webhook is an API endpoint designed to be called by an outside service when an event occurs. Here's what you need to know about webhooks in Express.

Server-sent events are an alternative to websockets for pushing events from your Express server to your client. Here's how you can get started with server-sent events in Node.js with Express.

The switch statement is like a multi-tiered `if` statement that can execute different code for different cases. This tutorial shows you how to use the `switch` and `case` statements.

The `vue.config.js` file configures the Vue CLI. Here's what you need to know.

Vue components have lifecycle hooks just like React components. Vue calls these functions whenever it does certain things to your component.

Learn how to set classes on an element conditionally in Vue.js.

The `this` keyword, also known as a function's "context" or "scope", is a powerful but confusing concept. Here's how you can wrap your head around it.

Whether you should use `==` or `===` is a common cause of confusion in JavaScript. The TLDR is that you should use `===`, with one minor exception. Here's what you need to know.

You can get tomorrow's date using vanilla JavaScript, although it is often easier with a library like Moment.js. Here's what you need to know.