Programmatically Adding Properties to Objects in Javascript

Question

I am trying to programmatically add properties to an object. This case is a little bit different though, and I am not sure how to approach this issue.

Normally, to apply properties to an object I would apply it in this context:

var a = []
var len = result[0].length
for(m=0; m < len; m++){
  a[m] = "b" + m // creates b1-b17 usually, but if the results are shorter it will create them equal to the length of the results
}
const values = {}
for(g=0; g<len; g++){
  values[a[g]] = [];
}

This would add an empty array to each property "b1" through "b17" normally, but its dynamic, in case the results are shorter.

Now I would like to do the same thing to this code, but inside the "return" part only. Is there anyway that I can call that and input those variables programmatically like I have done previously?

const rowData = tableData.map(result => {
  for(var h in a){
    values[a[h]].push(result[h]);
  }
  return {
    //I want to put properties in here programmatically and dynamically like I did previously
  }
})

Thank you guys for your time!

creates b1-b17 usually Really? It should create something like b0-b17 — CertainPerformance
– CertainPerformance, Commented Jun 27, 2018 at 23:37
I would be much easier to understand what you are asking if you would provide some some input data for tableData and show what you want the output to be. — Mark
– Mark, Commented Jun 27, 2018 at 23:41
So you want each member of tableData to be turned into an array of b0..b17 type values? Not at all clear what you're trying tro achieve — Tibrogargan
– Tibrogargan, Commented Jun 27, 2018 at 23:43
@CertainPerformance it does create b0-b17, my bad. I didnt proof read that part. — CoreyG
– CoreyG, Commented Jun 27, 2018 at 23:44
Why isn't your "context" code const values = {}; for(g = 0; g<len; g++) { values["b"+g] = []; }? — Tibrogargan
– Tibrogargan, Commented Jun 27, 2018 at 23:49

Mark · Accepted Answer · 2018-06-28 00:11:28Z

1

You can turn an array like ['data1', 'data2', 'data3', 'data4'] into an object with dynamic keys like column1 using reduce(). For example:

let arr = ['data1', 'data2', 'data3', 'data4']
let obj = arr.reduce((a, c, i) => (a['column' + (i + 1)] = c, a), {} )

console.log(obj)

With that in hand, given an array of such arrays you can combine it with map() to get your final result:

let tableData = [['data1', 'data2', 'data3', 'data4'], ['data11', 'data22', 'data33', 'data44']]

// for each array in tableData make an object with reduce and  add it to the returned array   
let result = tableData.map(arr => arr.reduce((a, c, i) => (a['column' + (i + 1)] = c, a), {} ))

console.log(result)

answered Jun 28, 2018 at 0:11

Mark

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