You can declare a variable without an initial value:
let score
console.log(score) // undefined
score = 100
console.log(score) // 100
This is useful when you'll assign the value later, like inside a condition:
let message
if (hour < 12) {
message = "Good morning"
} else {
message = "Good afternoon"
}
But with const, you must assign immediately. Uninitialized const is a syntax error.