类数组

类数组（Array-like Object）不是数组类型，比如 arguments：

  1. function sum() {
  2.     let args: number[] = arguments;
  3. }
  5. // index.ts(2,7): error TS2322: Type 'IArguments' is not assignable to type 'number[]'.
  6. //   Property 'push' is missing in type 'IArguments'.

事实上常见的类数组都有自己的接口定义，如 IArguments, NodeList, HTMLCollection 等：

function sum() {
    let args: IArguments = arguments;
}