How to form a dynamic json array in nodejs?

Question

I have a set of values in my db. After reading that, my output will be like below.

FetchValues = 
 [{
 "Key": "123"
 "Value":"aa"
 "Type":"A"},
 {},
 {}
 ]

I need to form a dynamic json array like below after fetching the values from DB.

 {
 "A":{
 "123" : "aa"
 },
 {
 "B": {
 "124" : "bb"
 }
 }
 var Json = {}
for(k=0;k<fetchValues.length;k++)
{
 Json.push({ fetchValues[k].Type 
 : {
 fetchValues[k].Key : fetchValues[k].Value
 }
 })

But it gives error. Kindly help on this.

• Philip Raath: Please include the error you are receiving.
• Priyanka: It is syntax error while trying to form a json and push in to an array
• AlexH: By JSON, do you mean object?

Answer 1

You may leverage destructuring syntax within Array.prototype.map():

const src = [{Key:"123",Value:"aa",Type:"A"},{Key:"124",Value:"bb",Type:"B"}],
 
 result = src.map(({Key, Value, Type}) => ({[Type]:{[Key]:Value}}))
 
console.log(result)

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Or (if your actual intention was to output an object, rather than array):

const src = [{Key:"123",Value:"aa",Type:"A"},{Key:"124",Value:"bb",Type:"B"}],
 
 result = src.reduce((acc, {Key, Value, Type}) => 
 (acc[Type] = {[Key]:Value}, acc), {})
 
console.log(result)

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Answer 2

@Yevgen Gorbunkov's answer is way better, but here's an approach using forEach:

const src = [{Key:"123",Value:"aa",Type:"A"},{Key:"124",Value:"bb",Type:"B"}];
let res = {};
src.forEach(element => res[element.Type] = { [element.Key]: element.Value });