Async functions were introduced in the 2017 edition of the JavaScript language spec. Async functions differ from normal JavaScript functions in 2 major ways:

Mongoose 5.6.0 was released last week. This new release has 12 new features, 2 performance improvements, and several docs improvements. The most interesting new feature is immutable properties. The idea is that marking a property as immutable means that property cannot change after the document is created.

JavaScript arrays are an essential part of the language. Fundamentally, an array is a value that stores an ordered list of other values. But JavaScript arrays come with a lot of nuances and surprises. In this article, I'll provide an overview of what you need to know about JavaScript arrays.

Puppeteer is a powerful automation library for Google Chrome. With Puppeteer, you can launch a Chrome browser that you have full control over from Node.js. This makes UI testing easy: your client-side app runs in a real browser, no need to worry about the painful quirks of Jest attempting to mimic a browser in Node.js. Puppeteer runs in headless mode by default, which means the Chrome window isn't visible. But you can still take screenshots in headless mode, or you can disable headless mode and watch your tests click through your app.

The JSON.stringify() function is the canonical way to convert a JavaScript object to JSON. Many JavaScript frameworks use JSON.stringify() under the hood: Express' res.json(), Axios' post(), and Webpack stats all call JSON.stringify(). In this article, I'll provide a practical overview of JSON.stringify(), including error cases.

Promises are a built-in concurrency primitive that's been part of JavaScript since ES6 in 2015. The Promise class has been included in Node.js since v4.0.0. That means, unless you're on an unmaintained version of Node.js, you can use promises without any outside libraries.

Private class fields are a Stage 3 TC39 proposal. Even though they're still experimental, you can use private class fields in Node.js 12 without flags or transpilers. In this article, I'll explain the basics of private class fields and how they interact with existing paradigms, like Object.keys() and assert.deepStrictEqual().

When running MongoDB in production, you may see queries that should be fast, but instead are exceedingly slow. For example, my Node.js apps have seen a findOne() on a collection with only 1 document take over 1 second.

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