You can concatenate a first name and last name into a single string using different methods in JavaScript.

Method 1: Using the `+` Operator

let firstName = "John";
let lastName = "Doe";
let fullName = firstName + " " + lastName;
console.log(fullName); // Output: "John Doe"

Simple and direct method using `+` for string concatenation.

Method 2: Using Template Literals (ES6)

let firstName = "John";
let lastName = "Doe";
let fullName = `${firstName} ${lastName}`;
console.log(fullName); // Output: "John Doe"

Best practice: More readable and efficient than `+` operator.

Method 3: Using `concat()` Method

let firstName = "John";
let lastName = "Doe";
let fullName = firstName.concat(" ", lastName);
console.log(fullName); // Output: "John Doe"

Uses `.concat()` method to merge multiple strings.

Method 4: Using `join()` (Best for Arrays)

let nameArray = ["John", "Doe"];
let fullName = nameArray.join(" ");
console.log(fullName); // Output: "John Doe"