CODEWITHSUNDEEP
promise
Bastian
Bastian

Reputation: 207

JS promises: How to chain `then` calls?

I am trying to fetch some data, rework the object format and safe it in state. My last .then does not get the data from second one. I don't understand why this is the case.

fetch("http://myserver/switches")
    .then(response => response.json())
    .then(data => {
      a = data.map(item => {
        var obj = {}
        obj = {value: item.switch, label: item.switch}
        return obj
      })
      console.log(a)
    })
    .then(data => {
      console.log(data)
      this.setState({ switches: data})
      console.log(this.state.switches)
      })

console log:

 >(5) [{…}, {…}, {…}, {…}, {…}]
 >undefined
 >undefined

Upvotes: 0

Views: 47

Answers (1)

marcodt89
marcodt89

Reputation: 411

Try to add in the second then() a statement return a This will provide a as a parameter for the last then().

fetch("http://myserver/switches")
.then(response => response.json())
.then(data => {
  a = data.map(item => {
    var obj = {}
    obj = {value: item.switch, label: item.switch}
    return obj
  })
  console.log(a)
  return a;
})
.then(data => {
  console.log(data)
  this.setState({ switches: data})
  console.log(this.state.switches)
  })

Upvotes: 1

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