How to Map Array values from one Array to Another Array JavaScript?

Question

This is my Code. Where I want to Pass the Values of kvArray to Second Array.

var kvArray = [{key: 1, value: 10}, 
               {key: 2, value: 20}, 
               {key: 3, value: 30}];

var reformattedArray = kvArray.map(obj => { 
   var payload = {};
   payload["rt"];
   payload["do"];
   payload["f1"];
   payload[obj.key] = obj.value;
   console.log(payload["rt"]);
   return payload;
});

The console.log is coming undefined. Can anyone help here? I am pretty new to Map function.

I want to Print this result.

 payload["do"]=10
 payload["f1"]=20
 payload["f2"]=30

Solution 1

var kvArray = [{key: 1, value: 10}, 
               {key: 2, value: 20}, 
               {key: 3, value: 30}];

var reformattedArray = kvArray.map(obj =>{ 
   var payload = {};
   const mapping = [null, 'rt', 'do', 'f1']; 
   const key = mapping[obj.key];
   payload[key] = obj.value;
   return payload;
});
console.log(reformattedArray);

Solution 2

You could use a destructuring assignment and build a new object with computed property names.

For the final keys, you could use an object keys with corresopnding keys to the the keys of the given object.

var kvArray = [{ key: 1, value: 10 }, { key: 2, value: 20 }, { key: 3, value: 30 }],
    keys = { 1: 'rt', 2: 'do', 3: 'fi' },
    result = kvArray.map(({ key, value }) => ({ [keys[key]]: value }));
    
console.log(result);

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Solution 3

I'm not sure what format you want.

try the code below：

var kvArray = [{ key: 1, value: 10 },
  { key: 2, value: 20 },
  { key: 3, value: 30 }];
var reformattedArray = kvArray.map(obj => obj.value);
console.log(reformattedArray)

the result will be:

[ 10, 20, 30 ]

Comments

[Lesleyvdp]

You are assigning payload[1], payload[2] and payload[3] when you are referring to obj.key in your map function. Thus payload["rt"] remains undefined.

[NullPointer]

what value you want to store in payload["rt"] ?

[Nina Scholz]

please add the wanted result as well.

[codemt]

@NullPointer i want payload["rt"] = 10.

[Nina Scholz]

btw, it's quite unclear, if the wanted keys depends on the index or on the key values.

[codemt]

i have defined the keys of the array payload. and i want this output payload["rt"] = 10. like this.

[codemt]

this is helpful:). thank you so much. Just to pass the keys of 'rt','do' to the payload, it is better to map them by declaring them in another array. thats sweet :)

[Nurkartiko]

const mapping = [null, 'rt', 'do', 'f1']; what is null for?