The first example: as It’s not an assertion, right? as It’s a forced conversion, which means you know what you want to do. Of course, ts will let you compile it.
The second example seems to have been done originally, right? color You don’t have to; colour is another attribute
The reason why it was not used before is that ts has a unique check for object literals

1. as is forced type conversion, which forces a variable to be used as another type. You are responsible for any problems during runtime.

2. The detection logic of using object literals to assign objects is different from the mechanism of using variables to assign objects.

interface SquareConfig {
    color?: string;
    width?: number;
}

function test(config: SquareConfig): void {}

let a = { colour: "red", width: 100 };
// 不报错, typeof a 与 SquareConfig 类型兼容
let b: SquareConfig = a; 

// 报错，声明 c 是 SquareConfig 类型但是给了不存在的属性
let c: SquareConfig = { colour: "red", width: 100 }; 

// 报错，原因和上面类似
test({ colour: "red", width: 100 })

// 不报错，强制把这个对象字面量当 SquareConfig 类型使用，出问题你自己背锅
let d: SquareConfig = <SquareConfig> { colour: "red", width: 100 };