为 const object 的属性赋值是否应该产生 typeError？

Question

 const sendData = result => { result.centers.forEach(center => { const data = { center_id, name, address, district_name, state_name, pincode, fee_type, sessions } = center; data.sessions = data.sessions.map(session => { return { date, available_capacity, min_age_limit, vaccine } = session; }) console.log(data); }) }

why does the above code produce the following error?

PS: Please ignore the line numbers.

UnhandledPromiseRejectionWarning: TypeError: Assignment to constant variable.
    at /home/ubuntu/Projects/Web/CowinTracker/server/app.js:69:17
    at Array.map (<anonymous>)
    at /home/ubuntu/Projects/Web/CowinTracker/server/app.js:67:39
    at Array.forEach (<anonymous>)
    at sendData (/home/ubuntu/Projects/Web/CowinTracker/server/app.js:56:20)

I tried changing const data to let data and same error occurred.

Answer 1

You can't destructure in your return statement.

You need to either destructure the session argument, or reference the session object and assign the properties to a new object.

 const data = { centers: [ { center_id: 1, name: 'One', address: '1 one street', district_name: 'one', state_name: 'one', pincode: '1111', fee_type: 1, sessions: [ { date: new Date(), available_capacity: 1, min_age_limit: 1, vaccine: "its gene therapy" } ] } ] } const sendData = result => { result.centers.forEach(center => { const data = { center_id, name, address, district_name, state_name, pincode, fee_type, sessions } = center; data.sessions = data.sessions.map(session => { return { date: session.date, available_capacity: session.available_capacity, min_age_limit: session.min_age_limit, vaccine: session.vaccine }; }) console.log(data); }) } sendData(data)

If you wanted to destructure the session argument you could do something like this.

data.sessions = data.sessions.map((( 
  date, 
  available_capacity,
  min_age_limit,
  vaccine,
}) => ({
    date,
    available_capacity,
    min_age_limit,
    vaccine,
}) 

})

If you're just cloning the object you could do the following.

data.sessions = data.sessions.map(session => ({
  ...session
}))