javascript - 为什么我可以将未知属性分配给 typescript 中的文字对象？

Question

  type ExpectedType = Array<{ name: number, gender?: string }>

  function go1(p: ExpectedType) {

  }  

  function f() {
    const a = [{name: 1, age: 2}]
    go1(a)                   // doesn't complain
    go1([{name: 1, age: 2}]) // complain 'Object literal may only specify known...'
    go1(['no matter'].map(n => ({name: 1, age: 2}))) // doesn't complain
  }

typescript 代码如上，我的问题是最后三行不一样吗？为什么一线可以通过，二线投诉，三线通过？
同样在 typescript 操场上:
playground

Answer 1

将 var a 分配给 go1() 的参数时，似乎将变量 a 分配给另一个 para 变量。在这种情况下，因为 a 的类型与参数变量类型兼容。但是如果将类型更改为 { name: number, 性别:字符串 }，你仍然会有类型错误。
当分配一个字面量对象作为参数时，这种情况下没有类型转换，因此编译器可以检测到这种类型错误。
更多详情请引用 here .

The basic rule for TypeScript’s structural type system is that x iscompatible with y if y has at least the same members as x. Forexample:

interface Named {
    name: string;
}

let x: Named;
// y's inferred type is { name: string; location: string; }
let y = { name: "Alice", location: "Seattle" };
x = y;

To check whether y can be assigned to x, the compiler checks eachproperty of x to find a corresponding compatible property in y. Inthis case, y must have a member called name that is a string. It does,so the assignment is allowed.