Void Functions

[00:00] Okay. Let's just build out what this has for us. So we're making a a logging system. So I'm gonna make a function called log info that, simply logs, but we're gonna have this prefix of info. And that that's what makes it a logging system.

[00:15] Right? And we're gonna make a log error and that's got a prefix of error. There's actually a console dot error that you can call. There's also a warn and an info and a dir and I feel like there are a couple others. But, and and oh, yeah.

[00:29] Group and time and, you know, there's a whole bunch of stuff you can do with console. But we're just gonna stick with log, here, for now. And then we've got, log with time stamps. So we're gonna create a time stamp and log that. K.

[00:42] That's cool. And then we'll log all those and we'll export them. Alright. Great. So we've got our info, we've got our error, we've got our time stamp.

[00:50] Everything is good. What does this have to do with void? Well, you'll notice the AI actually kinda did this for us and and Marty the money bag was here telling you to do this as well. But explicitly typed each one of these as void. What that does is it means that I cannot return anything.

[01:04] I can't I can't return anything, except for undefined because undefined is technically the same thing that you would get if we return nothing, if you don't have a return statement. So, we're getting, a void return here. Now what's kinda interesting is here we have our type is defined as returning void. If I remove that, then our type is actually technically defined as returning undefined. So you can see how these concepts kind of overlap a little bit, but we don't actually need to return undefined.

[01:35] And without that, it's going to say that we returned void, which effectively, all that really does is it means that I can't do anything to this. Like, it it returned nothing. There's nothing that I can call, on here. I cannot assign it to a value and have that value, have anything on it. There's there's just nothing that I can do with it.

[01:56] That value is void. It's it's just nothing. That's why I say we're talking about nothing because void explicitly, by typing it explicitly or just not returning anything from your your function, you're saying just nothing for this. Void is actually not just a TypeScript thing either. Void is a feature of JavaScript.

[02:16] So you can actually say, const x equals void zero. That is a this is a fun little, trivia here. Even today, we still have bundlers and JavaScript minifiers that try to take the code that you write and make it as small as possible. Use as few characters as possible because it will load faster for whoever is downloading your website. And so, we can have this, const y equals undefined or we can have, const equals void one of these and we can, like, eliminate all the characters that we possibly can and everything.

[02:55] One of these is shorter than the other. And so actually, a minifier is going to go through your code and it's gonna find everywhere it finds undefined and it's going to change it for void zero, because that is faster. You can it's not just zero. You can have it be a string, but by adding void to it, it just makes this expression undefined regardless of what what it returns. You could say, date dot now which returns the time stamp for the current date.

[03:21] And with without the void, you're gonna get number. But if you add a void, it turns that into undefined. Like I said, this isn't something you do a whole lot. Pretty much the only time I ever do this is when I, do some sort of asynchronous thing. I call a function that returns what's called a promise and I want to ignore that promise.

[03:42] Typically, you would put an await there to wait for that promise to finish and and everything. Now, if I want to ignore that result, I just put void to say, no, I didn't forget the await keyword. I literally don't care what this promise returns or or when it results or anything. That is something we're gonna talk about way later. So if that kinda went over your head, don't worry about it.

[04:01] You typically don't use void and you typically don't even explicitly type your functions as returning void. You just don't return anything and then they're void. So if you see something that says void, now hopefully you understand void just means nothing into the void. Alright. Great job on that one.

[04:18] We'll see you in the next

[00:00] Okay. Now it's time to talk about nothing. No, about void. Void is kind of nothing. It's like null and undefined, but, like, another version of those things.

[00:10] And it's actually not something that I ever really saw in JavaScript itself very often. But now I see it a fair bit more in TypeScript, in part because of what happens when you don't have a return. Oh, okay. I'm spoiling stuff. I'm gonna let you just work on this exercise, play around with it a little bit, get your brain open to the idea in the problem space, and then we'll go through the solution, once you've played around with this a bit.

[00:34] So we'll see you when you're done.

Learning to program can feel overwhelming. There are countless tutorials, boot camps, and YouTube videos all pulling you in different directions, and most of them assume you already know something.

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## Expressions & Output

Every program needs a way to tell you what it's doing. Without output, you're flying blind-- writing code with no way to verify it works. This is the very first skill you need as a developer.

In this section, you'll get your programs talking back to you while learning the building blocks of every piece of code you'll ever write:

- Outputting values with `console.log`
- String expressions and concatenation
- Number expressions and arithmetic operators
- Escaping special characters in strings
- Template literals with interpolation and multiline support

## Variables

Hardcoded values can only get you so far. Real programs need to store, reference, and update data as they run. Without a solid understanding of how variables work, you'll constantly be confused by unexpected behavior.

Variables are foundational to every program you'll ever write. Here you'll learn how to declare them, when to use each type, and a critical nuance that trips up even experienced developers:

- Declaring variables with `let` and `const`
- Naming conventions and casing (camelCase, SCREAMING_SNAKE_CASE)
- Reassigning values with `let` and compound operators like `+=`
- The important distinction between reassignment and mutation
- Why `const` doesn't always mean the value can't change

## Primitive Types

JavaScript has types whether you think about them or not. Every value in every variable carries a type, and ignoring that fact leads to bugs that are hard to track down. TypeScript makes these types explicit, catching entire categories of errors before your code ever runs.

This section introduces you to all seven primitive types and how TypeScript helps you work with them safely:

- Explicit type annotations with `number`, `string`, and `boolean`
- The difference between `null` and `undefined`
- Special types: `bigint` for arbitrarily large numbers and `symbol` for unique identifiers
- Type coercion and why it can surprise you
- Floating-point precision and practical considerations for working with numbers

## Comparisons & Boolean Logic

Making decisions is at the heart of every program. Should this button be enabled? Does this user have access? Is the cart empty? All of these questions boil down to comparisons and boolean logic.

Getting comparisons wrong leads to subtle bugs that are painful to debug. This section gives you the tools to write conditions that behave exactly as you'd expect:

- Loose equality (`==`) vs. strict equality (`===`) and why you should almost always use strict
- Not-equal, greater-than, and less-than-or-equal-to operators
- Combining conditions with logical AND (`&&`), OR (`||`), and NOT (`!`)
- Order of operations with logical operators
- Using parentheses to make complex conditions explicit

## Truthiness & Falsiness

JavaScript has a unique feature where every value has an inherent "truthiness" or "falsiness." This isn't a bug-- it's one of the most practical features of the language once you understand it. But misunderstanding it leads to some of the most confusing behavior new developers encounter.

Here you'll learn which values are truthy, which are falsy, and how to use this knowledge to write cleaner conditional logic:

- Coercing values to booleans with the `Boolean` constructor
- The double-not (`!!`) operator and when to use it
- Falsy values: `0`, `""`, `null`, `undefined`, `false`, and `NaN`
- Practical patterns like checking array length and optional values
- Avoiding common pitfalls with logical operators and coercion

## Functions

Up to this point, your programs run top to bottom and that's it. Functions change everything. They let you take a chunk of code, put it somewhere reusable, and call it from anywhere-- with different inputs each time.

Functions are the single most important building block for organizing and scaling your programs. This section takes you from writing your first function through passing functions as arguments to other functions:

- Function declarations with the `function` keyword
- Accepting parameters and specifying their types
- Return values and TypeScript's return type inference
- Arrow functions and implicit returns
- Passing functions as arguments to other functions
- Documenting your functions with JSDoc

## Type Inference & Arrow Functions

TypeScript is smart. You don't have to type everything explicitly-- TypeScript can often figure out the types for you by looking at your code. Knowing when to lean on inference and when to be explicit is a skill that makes your code cleaner and your development faster.

This section also covers arrow functions, a concise alternative syntax you'll see everywhere in modern JavaScript and TypeScript:

- How TypeScript infers return types from your function body
- When explicit return types help catch bugs earlier
- Converting function declarations to arrow functions
- Implicit returns for single-expression functions
- The hoisting difference between declarations and expressions
- Function expressions as first-class values

## Void & Never

Not every function returns something useful, and some code paths should never be reached. TypeScript has dedicated types for both of these situations, and understanding them helps you write more precise, self-documenting code.

This section introduces two TypeScript-specific concepts that complete your understanding of the type system's fundamentals:

- The `void` type for functions that don't return a value
- How `void` relates to `undefined` in practice
- The `never` type for functions that throw errors or never return
- Using `never` to enforce exhaustive checks
- Throwing errors to halt execution and signal failures
- Practical patterns for input validation with error throwing

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Void Functions

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