类型'{ label: string；confidence: string；}| undefined‘上不存在属性'confidence’

Question

当我试图解构以下函数的返回类型时：

const coreml = async (
  pathToImage: string,
): Promise<{label: string; confidence: string} | undefined> => {
  //body
};

因此：

const {label, confidence} = await coreml(/*path to image*/);

我得到了

'confidence' is assigned a value but never used.eslint@typescript-eslint/no-unused-vars
Property 'confidence' does not exist on type '{ label: string; confidence: string; } | undefined'.

Answer 1

函数的结果是{label: string, confidence: string}或undefined。哪一个在编译时是未知的。但是您不能将undefined解构为label和confidence，而typescript希望确保类型安全。这样就产生了错误。

原则上，解构的工作方式如下：

const temp = await coreml();
//temp is now either {"label": "foo", "confidence": "bar"}  or undefined

//but the next statements will throw an error, if temp is undefined
const label = temp.label;
const confidence = temp.confidence;

Typescript希望确保，此错误不会在运行时发生。因此，编译时的错误