Array.push() 不工作，推送后返回空数组

Question

I am using Vue project to my mini search system and its database is firebase. I would like to know if these is a language error or its library error. where the Array.push() is not working properly.

I could show only screen shot because it could not show in other reproduction when I reproduce the code.

let trainVal1 = []
  for(let n in dataTrainingVal) {
    console.log({key: n, ...dataTrainingVal[n]})
    trainVal1.push({key: n, ...dataTrainingVal[n]})
    console.log(trainVal1)
  }

thanks!

Answer 1

Just create a object for the {key: n, ...dataTrainingVal[n]} like var obj = {key: n, ...dataTrainingVal[n]} . Then push it.

var trainVal1 = []
  for(let n in dataTrainingVal) {
    var obj = {key: n, ...dataTrainingVal[n]}
    trainVal1.push(obj)
    console.log(trainVal1)
  }

try also var insted of let

Answer 2

you should change your code like below

let trainVal1 = []
  for(let n = 0; n < dataTrainingVal.length; n++) {
    console.log({key: n, data:dataTrainingVal[n]})
    trainVal1.push({key: n, data:dataTrainingVal[n]})
    console.log(trainVal1)
  }

Answer 3

The error is on the spread operator section. I have updated your code to a working solution.

 let trainVal1 = [] let dataTrainingVal = [1,2,3] for(let n in dataTrainingVal) { console.log(dataTrainingVal[n]) trainVal1.push({key: n, val: dataTrainingVal[n]}) console.log(trainVal1) }

Please note: Do not use for in loop for array iterations.

Note: for...in should not be used to iterate over an Array where the index order is important. Read More on MDN

Answer 4

It seems to work fine... the only missing piece is defining dataTrainingVal.

     let trainVal = []
       let dataTrainingVal = {firstname: 'Pedro', lastName: 'Juan'}
       for(let n in dataTrainingVal) {
          console.log({key: n, ...dataTrainingVal[n]})
          trainVal.push({key: n, ...dataTrainingVal[n]})
          console.log(trainVal)
       }

The o/p :

(2) [{…}, {…}]

0: {0: "P", 1: "e", 2: "d", 3: "r", 4: "o", key: "firstname"}

1: {0: "J", 1: "u", 2: "a", 3: "n", key: "lastName"}

length: 2