var name = "Alana"

name.slice(1,4);

// will give l, a, n
// 4-1=3 so you will get 3 characters
// 1 starts at the 2nd letter. 4 stops up to but not including the 5th letter

alert(prompt("Compose your tweet:").slice(0,140));
// allows you to compose your tweet up to 140 characters and no more