Type Assertion / Casting

• 基本上跟 Golang 的同概念
• 如下面例子，有兩種寫法：
  1. <type>something
  2. something as type

function getLength(something: string | number): number {
  if ((<string>something).length) {
    return (<string>something).length
  }
  return something.toString().length
}

function getLength2(something: string | number): number {
  if ((something as string).length) {
    return (something as string).length
  }
  return something.toString().length
}