JavaScript on Coderrob

JavaScript 'this' and Arrow Functions Explained

Mon, 27 Apr 2026 11:00:00 -0500

JavaScript functions do not all decide this the same way.

Regular functions usually get this from how they are called. Arrow functions do not create their own this at all.

This post is about two questions:

Where does a regular function get this from?
Why does an arrow function behave differently?

this is one of the easiest JavaScript concepts to misunderstand because it looks like scope.

It is not scope.

JavaScript Closures and Modified Closures Explained

Mon, 27 Apr 2026 10:00:00 -0500

Closures show up any time a JavaScript function uses a variable defined from outside its own curly braces.

That makes them common in callbacks, event handlers, timers, factory functions, and plenty of code that passes functions around.

This post is about two questions:

What is a closure?
What happens when a closed-over variable is modified before the function uses it?

The short version:

A closure happens when a function keeps access to variables from its surrounding scope, even after that outer scope has finished running.

JavaScript Hoisting Explained

Sun, 26 Apr 2026 10:00:00 -0500

Hoisting is JavaScript’s setup behavior for declarations.

It affects whether a function or variable can be used before the line where it appears in the file. That matters because function, var, let, and const do not all behave the same way.

This post is about two questions:

When does JavaScript create the name?
What value, if any, is available before the declaration line runs?

Hoisting is usually explained as “JavaScript moves declarations to the top.”

JavaScript Var, Let, and Const Explained

Sat, 25 Apr 2026 10:00:00 -0500

Most JavaScript code starts with a simple act: you give a value a name. We call that a variable declaration.

That sounds small, but the way you create that name affects how the rest of your code can use it. A variable might be available only inside a small “if” block, across an entire function, or in places you did not really mean to share it.

That is why var, let, and const are worth understanding before the code gets complicated.

JavaScript Promise

Wed, 22 Oct 2025 21:00:00 -0500

A Promise is a guaranteed placeholder value for what a function or series of functions will return.

It’s a promise to return a value eventually.

The function swears this time is different. You can trust it. It swears it’ll get it back to you in no time.

If you haven’t already, check out my post on JavaScript Callbacks where we dove into callback hell and why we desperately needed something better. Spoiler: Promises are that something better.

Rollup, UUID, and Error Crypto getRandomValues() Not Supported - Solved

Sat, 24 Aug 2024 00:32:53 -0500

I ran into this error while using Rollup and the uuid package:

Error: Crypto.getRandomValues() not supported. See https://github.com/uuidjs/uuid#getrandomvalues-not-supported

The problem? It boiled down to this small mistake in my Rollup config:

// rollup.config.js
plugins: [
 nodeResolve({
 extensions: ['.ts', '.js'],
 exportConditions: 'node', // Wrong: should be an array
 }),
 // Other plugins...
],

The solution was simple. exportConditions needs an array, not a string:

// rollup.config.js
plugins: [
 nodeResolve({
 extensions: ['.ts', '.js'],
 exportConditions: ['node'], // Fixed: now it's an array
 }),
 // Other plugins...
],

TypeScript would’ve caught this, but in plain JS, it slipped through. Lesson (re)learned. Always verify.

JavaScript Spread Syntax Explained

Thu, 03 Mar 2022 21:28:27 -0600

The JavaScript spread ... syntax is amazing.

What it does is let you take the individual items from an array, or the individual properties from an object, and spread them out into another place.

That “another place” might be:

a new array
a new object
the arguments being passed into a function

When I first learned to use spread syntax I was a little confused about what it was actually doing. The three little dots looked simple enough, but JavaScript has a long history of making simple-looking things weird.

JavaScript Callbacks

Mon, 03 May 2021 15:00:00 -0500

Brief History of Callbacks

It all starts with the callback function.

A callback function is just a plain JavaScript function that is passed into another function as an argument.

That’s it. Nothing special.

This callback function can be used to return data, or to signal that some event took place.

If you’ve worked with web development you’ve definitely crossed paths with callbacks.

Think of a button click event for a web page.

JavaScript Function Parameters and Arguments Explained

Thu, 17 Sep 2020 00:46:15 -0500

JavaScript Function Signatures

Alright, you’ve probably seen functions before. Something like this maybe?

 function doSomething(name, desc, task) {
 // did something
 }

This function, named doSomething, takes three parameters as part of its function signature. These parameters named name, desc, and task are the names of the values being sent into the function.

I’m going to use a sportsball reference here so be warned. You can think of the function as a net that gets various types of objects tossed into the hoop ( ) where it triggers sports points.