Comments

JavaScript, Go, Rust, Swift, and Java all share the exact same comment syntax: // for a single line, /* ... */ for a multi-line block (Rust and Swift both allow nesting block comments, unlike JS/Go/Java). There's nothing new to learn here — the real difference only shows up once a comment sits right above a declaration and becomes a doc comment: JSDoc in Node.js, godoc in Go, rustdoc in Rust, doc comments in Swift, Javadoc in Java.

Line and block comments

// this is a line comment
 
/*
 this is a block comment
*/

package main
 
func main() {
	// this is a line comment
 
	/*
	   this is a block comment
	*/
}

fn main() {
    // this is a line comment
 
    /*
     this is a block comment
    */
}

// this is a line comment
 
/*
 this is a block comment
*/

void main() {
    // this is a line comment
 
    /*
     this is a block comment
    */
}

Doc comments: JSDoc, godoc, rustdoc, Swift, Javadoc

/**
 * Returns a greeting for the given name.
 * @param {string} name
 * @returns {string}
 */
function greet(name) {
  return `Hello, ${name}!`
}
 
console.log(greet('Go')) // Hello, Go!

package main
 
import "fmt"
 
// Greet returns a greeting for the given name.
func Greet(name string) string {
	return "Hello, " + name + "!"
}
 
func main() {
	fmt.Println(Greet("Go")) // Hello, Go!
}

/// Returns a greeting for the given name.
fn greet(name: &str) -> String {
    format!("Hello, {name}!")
}
 
fn main() {
    println!("{}", greet("Go")); // Hello, Go!
}

/// Returns a greeting for the given name.
/// - Parameter name: the name to greet.
/// - Returns: the greeting string.
func greet(_ name: String) -> String {
    "Hello, \(name)!"
}
 
print(greet("Go")) // Hello, Go!

/**
 * Returns a greeting for the given name.
 *
 * @param name the name to greet
 * @return the greeting string
 */
String greet(String name) {
    return "Hello, " + name + "!";
}
 
void main() {
    IO.println(greet("Go")); // Hello, Go!
}

A Go doc comment must start with the exact name of the identifier it describes (Greet returns...) for go doc/godoc and editors to recognize it; JSDoc uses a /** ... */ block with @param/@returns tags so tools like VS Code and TypeScript can infer types and show hints. rustdoc (///) doesn't need to start with the function's name the way Go does, and it renders real Markdown (including runnable doctests). Swift uses /// with - Parameter/- Returns markers so Xcode/DocC can show Quick Help. Javadoc uses /** ... */ with @param/@return tags, even for top-level methods in a Java 25 compact source file.