The + operator joins strings:
let first = "Hello"
let second = "World"
console.log(first + " " + second) // "Hello World"
Watch out when mixing strings and numbers:
console.log("Score: " + 100) // "Score: 100"
console.log("5" + 3) // "53" (not 8!)
If either operand is a string, + concatenates instead of adding. Use template literals to avoid confusion:
console.log(`Score: ${100}`) // Clearer intention