• Static type checking is what works before the code runs.
• Variables declared by let are only available inside the block where they’re defined and variables declared by var are available throughout the function in which they’re declared.
• The difference between interface and type is that interface is extendable and type is not.
• The never type is assignable to every type; however, no type is assignable to never  (except never itself).
• JavaScript object keys are always coerced to a string, so obj[0] is always the same as obj["0"].

Non-null assertion operator:

Passing null to this function will throw an error

function liveDangerously(x?: number | null) {
  // No error
  console.log(x!.toFixed());
}
liveDangerously(1)