TypeScript Version: 3.0.0-dev.20180623

Search Terms: typescript unknown equality guard

Code

let x: unknown; // reproduces with const too
if (x === 5) {
    let y = x.toString(10);
}

Expected behavior:
x inside of the if block to be of type 5, y to get type of string, everyone happy.
Actual behavior:
x inside of the if block is still of type unknown, I get an error for x being of type unknown and therefore does not have a property toString.
Playground Link: N/A (dev build)

Related Issues: #24439