How to copy some properties from an object to another

Question

I have an object listData with the following values:

{
    "TestId": 2,
    "CurrentTestVersion": 1,
    "TestNumber": "2015-29059",
    "SharingData": 1.000000,
    "ThresholdValue": 0.0,
    "ExpireDate": "2022-12-31T00:00:00",
    "UpdateDate": "2021-10-01T00:00:00",
    "TestCurrency": "INR",
    "TestCode": "44300",
    "TestUCode": "",
    "IndexType": "LME",
    "IndexCode": "EUR",

}

I need to create one more object with only selected fields like:

{
    "TestId": 2,
    "CurrentTestVersion": 1,
    "ThresholdValue": 0.0,
    "ExpireDate": "2022-12-31T00:00:00",
    "TestCurrency": "INR",
    "TestCode": "44300",
    "TestUCode": "",
}

I have checked with What is the most efficient way to copy some properties from an object in JavaScript?, which works well with JavaScript but not with TypeScript; any better ways to selectively copy properties?

What _specific problem_ have you had adapting those JS answers to your use case? The runtime behaviour is the same so it should just be a case of adding type information, no? Give a [mre]. — jonrsharpe, Jan 06 '22 at 09:31
Could you use `Pick`? Docs: https://www.typescriptlang.org/docs/handbook/utility-types.html#picktype-keys — André Krosby, Jan 06 '22 at 09:32

Mohsen Mahoski · Answer 1 · 2022-01-06T09:56:19.343

1

I think you need a mapper something like this:

  const objMapper = (obj: { [key: string]: string | number }, keys: string[]) => {
    const result: { [key: string]: string | number } = {};

    for (const k of keys) {
      if (obj[k]) {
        result[k] = obj[k];
      }
    }

    return result;
  };

and you can call it like this:

const result = objMapper({
    "TestId": 2,
    "CurrentTestVersion": 1,
    "TestNumber": "2015-29059",
    "SharingData": 1.000000,
    "ThresholdValue": 0.0,
    "ExpireDate": "2022-12-31T00:00:00",
    "UpdateDate": "2021-10-01T00:00:00",
    "TestCurrency": "INR",
    "TestCode": "44300",
    "TestUCode": "",
    "IndexType": "LME",
    "IndexCode": "EUR",

}, ["TestId", "CurrentTestVersion", ...]);

and it will return your custom object

edited Jan 06 '22 at 09:56

answered Jan 06 '22 at 09:46

Mohsen Mahoski

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Thanks for the suggestion, it works well with static JSON, but when I try with dynamic JSON object , the result is null. var PistData = this.TestDetails.userDetails; const result = this.objMapper({ PistData }, ["TestId"]) console.log("result pist:", result); – Kiran Narayan Jan 07 '22 at 02:48
Can you tell me what will be the result if you change ```result = this.objMapper({ PistData })``` to ```result = this.objMapper({ ...PistData }, ['TestId']);``` ? – Mohsen Mahoski Jan 07 '22 at 07:11

vaira · Answer 2 · 2022-01-06T09:56:57.307

You don't need to remove the extra property, since you are working with type script, you must have two interface/class to represent respective the structures. eg:

        AllProperty ap; // source
        SomeProperty sp; // target
        
  // Sine in your example your object does not have any reference type property , 
 // you can simply transfer the values to a new object.
        
        var sp = Object.assign(sp, ap) as SomeProperty;

If you want to remove properties for some other reason (data being sent through API)

you can either use 'delete' keyword, ... spread operator etc

How to copy some properties from an object to another

2 Answers2