是否可以在解构之前检查对象是否可用？

Question

I have an object of values to Destructure , But before doing so i would like to check if the object is available,

const  { contactno, contactemail } =  this.props.app.user;

In this case the object user is not available always, Due to this I am getting following error,

TypeError: Cannot read property 'contactno' of undefined.

Hence, Is there nay way to check if the object is available before Destructure ?

Answer 1

使用 AND 和 OR 运算符，您可以像这样安全地解构对象。

const  { contactno, contactemail } =  (this.props.app && this.props.app.user) || {};

Answer 2

Use it like below (nested destructuring). If user is undefined the default to {} in destructuring. when user is undefined, the contactno, contactemail also undefined with this.

const  { user: { contactno, contactemail } = {} } =  this.props.app;

Answer 3

你可以这样做

const  { contactno, contactemail } =  (this.props.app && this.props.app.user) ? this.props.app.user : {} ;

Answer 4

You can also use the double question mark (nullish coalescing) operator

const { contactno, contactemail } = this.props.app.user ?? {};

Reference: https://sebhastian.com/javascript-double-question-mark/