Preserving original properties in Typecript object class

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How do I preserve the original properties of a class object when mapping with the new object.

Let's say I have a class with the following property.

export class User{
 public name: string;
 public age: number;
 public internalId: number;
}

Following is where I am assigning values from call back subscribe() function

this.userService.getUnratedJobNotification().subscribe(
            (data)=>{
                if(data && data.length > 0){
                    this.User = data;
                }
        });

Now the data I receive from service only contains a name and age. Not internalId property.

After assigning via subscribe function, I only left with name and age.

I don't really know if this question was answered before or at least I don't really know what the right way to ask.

With Object.assign.

this.User = Object.assign({}, this.User, data);

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You can use Object.assign to copy all properties from your returned object into an actual User object.

I recommend using RxJS' map operator before subscribing:

this.userService.getUnratedJobNotification().pipe(
  map(data => Object.assign(new User(), data))
).subscribe((user: User) => {
  this.User = user;
});

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You can also use lodash merge to deal with complex entities:

var object = {
  'a': [{ 'b': 2 }, { 'd': 4 }]
};

var other = {
  'a': [{ 'c': 3 }, { 'e': 5 }]
};

_.merge(object, other);
// => { 'a': [{ 'b': 2, 'c': 3 }, { 'd': 4, 'e': 5 }] }

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Replace this.User = data; with this.User = {...this.User, ...data};

this.userService.getUnratedJobNotification().subscribe(
  data => {
    if (data) {
      this.User = { ...this.User, ...data };
    }
  });

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Comments
  • Which I will assign later, maybe numbers. 1st I load this data, then render HTML elements, based on users interaction with each set of the object I will flag the internalId. which then be processed for submission based on this flag.
  • So what does this pipe do?
  • pipe is how you apply RxJS operators to your observables. See stackoverflow.com/questions/48668701/what-is-pipe-for-in-rxjs.
  • Still, it over writes the original class properties.
  • Not sure to follow. Can you maybe create a StackBlitz to reproduce the issue?
  • I mean, what I want is after observable call, I should see the original property internalId so that I can later use it for submition back to API. if this property is not there, I cannot actually submit since this will throw property not found exception.
  • I removed the check data.length > 0 because an object does not have length property.