问结构类型不是鸭子类型。

EN

interface LabelledValue {
    label: string;
}

function printLabel(labelledObj: LabelledValue) {
    console.log(labelledObj.label);
}

let myObj = {size: 10, label: "Size 10 Object"};
printLabel(myObj);

interface Duck {
    typing(): void;
}

const porky = {} as Duck;

try {
    porky.typing();
} catch (error) {
    console.log(error); // TypeError: porky.typing is not a function
}

const isDucky = (it: { typing?: () => void }): it is Duck =>
    typeof it.typing === 'function';

const daffy = {
    typing: () => console.log('tappity tap tap')
};

if (isDucky(daffy)) {
    daffy.typing(); // tappity tap tap
}