let and const have introduced block-level scoping to JavaScript, and I now understand the difference. But I'm yet to find a compelling real-world example where let has an advantage over var.
What does block-scoping offer in practical terms (illustrated by example)?
1) It creates consistency with other languages:
With var it is often quite unclear where a variable is defined and where we can access it and were not:
if(false) {
var a = 1;
} else {
a = 2; // wtf
}
alert(a);
With let its obvious:
let a;
if(false) { a = 1; } else { a = 2; }
2) It allows useful closuring in for loops:
for(var i = 0, i < 10; i++)
setTimeout(() => console.log(i), 100);
// 10 10 10 10 ...
for(let i = 0, i < 10; i++)
setTimeout(() => console.log(i), 100);
// 0 1 2 3 4 5 6 ...
