This article lists several topics that will help you understand quickly if you are a JavaScript developer. Many tutorials start from scratch. But if you already know something else, why not compare them? Rust These are differences that I wished I could refer to before starting Rust, kept short. Disclaimer! I’m very far from being well versed in Rust. These are how I interpret them and no more than that. Rust has quite a vast documentation, so if you’re looking for details, please google them instead. . My goal is to list the important things so that you (and me in the future) can skip common programming concepts and focus on the differences based on the knowledge you already know. The book is a great starting point for learning rust Types Rust is a typed language, so it’s closer to TypeScript. You’ll have a much better experience if you already know TS. For the most part, both syntaxes are similar ( ) horray! variable_name: Type snake_case Yep, no getting around it. What’s this symbol? 1. Question mark ( ) ? You may see after a function call like so: . ? my_function()?; No, it’s not optional chaining. . You'll commonly see this when dealing with asynchronous functions. More about this later. It’s an error handling magic for functions that can fail (fallible functions) Documentation 2. Exclamation mark on functions ( ) ! Example: println!("{:?}", my_variable); . JS doesn't have anything similar to this. Macros are a way of writing code that writes other code. You can think of it like a custom syntactic sugar. Just use it if the function example shows it. This indicates that it’s a macro 3. The symbol & Example: &your_variable To get the reference. You’ll know this if you used low-level languages like C. More later. Syntax Semicolon ( ) at the end of each line is mandatory ; Exception: Semicolon ( ) is not mandatory on the last line of a function. In this case, . ; it’s a shortcut for returning that line . Not a big deal. Function syntax is slightly different fn foo(num: i32) -> i32 {
  3 // See no.2
  // or
  // return 3;
} . It’s also called Decorator syntax also different Attributes. What are these keywords? struct It’s a JSON object. (Ok, it’s more complicated but see the docs for that) type Person = {
    firstName: string;
    lastName: string;
};


struct Person {
    first_name: String,
    last_name: String,
} trait An interface impl . The closest thing we have to this are classes. It's the link between a and a type. An implementation of trait trait I’ve not used it enum . But you can store data in it. It’s pretty neat and quite an important concept to understand for async. Quite similar to Typescript enums in a way Console.log Not as easy, unfortunately. It’s more similar to printf from other languages println!("{:?}", my_variable); Library/Dependencies Use instead of . (instead of using a command like ) Cargo.toml package.json You’ll want to add them manually yarn add Documentation Example: [dependencies]
chrono = "0.4"
egg-mode = "0.16.0" Importing . It’s quite different from JS but basically: Rust has modules They’re sort of like namespaces. Here’s a breakdown on importing a dependency: use rocket::serde::{json::Json, Deserialize, Serialize}; - use this instead of use import - this is the package name rocket - accessing a module :: - the module name serde - things to actually import {json::Json, Deserialize, Serialize} Some more syntax: use chrono::prelude::*; use rusqlite::Result; Importing from local files Best explanation: https://doc.rust-lang.org/rust-by-example/mod/split.html Use to the path/file you want to import to make the compiler include the module. mod Then to import it. Note: automatically imports it too. In this case, you will need to prefix it with . use mod crate Example: use crate::your_file_or_module; Note: is a special filename which acts like mod.rs index.js See the link above for examples. Const vs let In JavaScript, you’d use most of the time because it’s immutable. const In Rust, you’ll want to use instead. This is immutable by default. If you want it to be mutable, use keyword. is reserved for actual constants (so you can’t calculate the value from another variable) let mut const let immutable_variable = ...;
let mut mutable_variable = ...;
const MY_CONSTANT = "CONSTANT"; Library Documentation If the Github repo doesn’t link to the documentation page, you can probably get to it like this: Asynchronous By far, the 2 most confusing topics are and . I would recommend reading more comprehensive documentation for these. Let’s talk about futures first. futures ownership is like a . Unlike JS, Rust has a type for the result of the promise/future called . It also accepts the error type on the generics (I wish JS has this). You can also use on its own without . Future Promise Result Result future Executing (or “consuming”) Future The standard library is quite bare-bones so you’ll need to import something else (Think for JS). You need an executor to run a . I recommend using and reading their documentation. bluebird future https://github.com/tokio-rs/tokio to await a function .await Interesting syntax, yeah? Actually quite nice since you don’t have to wrap it with brackets like in JS. async_function().await; Handling Result . Rust is safe so you’ll need to handle everything. Yes, all error cases unlike JS! This is another important one The enum has and . If the future is successful, it returns , otherwise . Result Ok Err Ok Err The most comprehensive way to handle both cases: let f = File::open("hello.txt");

let mut f = match f {
    Ok(file) => file,
    Err(e) => return Err(e),
}; The above uses the . pattern matching syntax which is also great This is quite verbose so there are 2 common ways to shorten it: Using .unwrap() Example: let my_value = async_function().await.unwrap(); This gets the success value and panics if Err Use this only when you’re confident that it won’t error or in test environment. Using the syntax ? This passes the error up. So your function needs to be able to return an error, too (either a or an ) Result Option See this for example and its equivalent Ownership & References Heard of the borrow checker? Nothing much for me to say here. It’s the hardest thing on this list since it’s unique to rust. And if you’ve never handled references before, this topic might be a bit steep. Thankfully the rust book saves the day once again Basically: Read part 4.1, 4.2 and 4.3 And that’s it! This list is actually shorter than I expected. I hope it’s useful for your journey. See a mistake or have any suggestions? Let me know! Like what you see here? Find or . more of my post check my startup Also Published Here

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