CODEWITHSUNDEEP
typescript
jong shin
jong shin

Reputation: 794

Property 'XXX' is missing in type 'YYY' but required in type 'ZZZ'

I'm having trouble initializing class properties. I have typescript code like this.

export class myClass  {
  a: number;
  b: number;
  public getCopy(anotherClass: myClass): myClass {
    return {
      a: anotherClass.a,
      b: anotherClass.b
    };
  }
}

But I'm getting this error message.

Property 'getCopy' is missing in type '{ a: number; b: number; }' but required in type 'myClass'

Why is it thinking getCopy() is a property? I have C# background and C# does not require to initialize functions. Is there a way to create a class instance and initialize properties without initializing functions? I'm looking for an easier way like C# code below.

var newInstance = new myClass()
{
  a = 1,
  b = 2
};

Instead of doing like this.

var newInstance = new myClass();
newInstance.a = 1;
newInstance.b = 2;

Or is this not possible with typescript?

Upvotes: 1

Views: 569

Answers (3)

Icepickle
Icepickle

Reputation: 12796

I don't really think you need a class for the code you provided, just describe your datastructure in an interface, say

interface DataStructure {
  a: number;
  b: string;
}

and then create an object which has these properties, say:

const instance: DataStructure = { a: 5, b: 'test' };

You can then use the interface as well as parameters for your functions or return values. It doesn't have to be a class, so for example:

function someFunction( b: DataStructure): void {
}

someFunction(instance); // works
someFunction({a: 10, b: 'test'}); // works
someFunction({a: 10}); // doesn't work, b is required

Upvotes: 0

Explosion Pills
Explosion Pills

Reputation: 191749

getCopy is a property of myClass. You are declaring it as a property of myClass. An instance of myClass could also be written using Object notation:

const myClassInstance = {
  a,
  b,
  getCopy,
}

Since getCopy is not optional on myClass, you must have this property and it must match the type of the myClass delcaration, so it must be a function.

All that being said, it's not entirely clear to me why you need an instance method that creates a copy of the class. You could just have this as a standalone function instead. Cloning the top level of an object can also be done in a few different ways including the spread operator, so you generally don't need to write your own function to do this either.

const myClass = new myClass();
myClass.a = 1
myClass.b = 2;
const myClassCopy = { ...myClass };

Upvotes: 1

Matej Vehar
Matej Vehar

Reputation: 96

Create new clone instance of myClass class:

public getCopy(anotherClass: myClass): myClass {    
  return Object.assign(new myClass(), {...});
}

Upvotes: 1

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