How to update only matching subset of object properties in TypeScript?

Question

Let's say I have two types that share some properties:

type A = {
  shared1: string;
  shared2: string;
  notShared1: string;
};

type B = { 
  shared1: string;
  shared2: string;
  notShared2: string;
};

Now, I just want to update the matching subset of properties for two of these objects:

class MyClass {
  private const a = {
    shared1: "s1",
    shared2: "s2",
    notShared1: "ns1"
  };

  // how can I achieve something like this:
  private const b = { ...a, notShared2: "ns2" } // but without the 'notShared1' property of a
}

My idea

I tried to .filter the first object by the matching keys but unfortunately the method itself doens't work:

private updateB() {
  this.b = { ...this.a.filter(Object.keys(b)) } // filter method not available, why? 
  // (the filter content is not correct, just for better understanding what I try to achieve here)
}

Answer 1

This is something you can do in JavaScript. Given your definitions of a and b, runtime objects can be updated like:

a = { shared1: "s1", shared2: "s2", notShared1: "ns1" };
b = { shared1: "not s1", shared2: "not s2", notShared2: "ns2" };

for (const key in a) {
  if (b.hasOwnProperty(key)) {
    b[key] = a[key];
  }
}
console.log(b);
// output: Object { shared1: "s1", shared2: "s2", notShared2: "" }