Here's one that TypeScript gets wrong. It's kind of a canonical example of a program that is difficult to get right in a type system. (It's how I found the Fl

Here's one that TypeScript gets wrong. It's kind of a canonical example of a program that is difficult to get right in a type system. (It's how I found the Flow example linked upthread.) let x: number[] = []; let y: Object[] = x; y.push('a'); let bad = x.pop(); // bad has type number but is actually a string.