The loop is executed at least once.

examples/intro/do_while.js
"use strict";

var n = 1;
do {
    n++;
    console.log(n);
} while (n < 1);

For example you ask a question and let the user guess. Every time you compare the answer to the expected answer. You will need to get the value from the user before the first compare, and then if it fails, ask the user again. If you use plain "while" then you'll have to read from the user once before the while-loop and then inside the loop too. OTOH if you use the "do-while" loop, it is enought to ask in the do-block.