Typescript: how to extend interfaces for nested field and assign value to object?

Question

Consider the following interfaces :

interface MyType1 {
  field1: string;
    options: {
        basicOption1: string;
        basicOption2: string; 
    };
}

interface MoreOptions {
    moreOptions1: string;
    moreOptions2: string;
}

I extend the field options of interface MyType1 :

interface MyType2 extends MyType1{
    options: {
        basicOption1: string; // How to remove it, yet declared in MyType1
        basicOption2: string; // How to remove it, yet declared in MyType1
        moreOptions1: string;
        moreOptions2: string; 
    };
}

If I omit lines : basicOptions1:string;and basicOptions2:string;, compiler complains. So, I add them. But, is it possible to remove them and only keep lines : moreOptions1:string; and moreOptions2:string; for the additional options.

Following, how could I assign an object of type Mytype2 from two objects of type MyType1 and MoreOptions ?

For example (Rq : I test other things but also unsuccessful) :

let myobj1: MyType1 = { field1:"field1", options:{ basicOption1:"basicOption1", basicOption2:"basicOption2" } };
let moreOptions: MoreOptions = { moreOptions1: "moreOptions1", moreOptions2: "moreOptions2" }

let myobj2: MyType2 = { ...myobj1, options: {...moreOptions} };

Answer 1

You can intersect the desired types for options property:

interface MyType2 extends MyType1 {
    options: MyType1["options"] & MoreOptions
}

Concerning MyType2 extends MyType1 and the error:

Existing properties in MyType1 like options have to be identical in MyType2, they do not get overwritten or merged in somehow. Other properties like field1 are automatically carried over.

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Following, how could I assign an object of type Mytype2 from two objects of type MyType1 and MoreOptions ?

You can use object spread, which will merge all objects and in case of equally named properties choose the right-most one (Playground sample):

declare const t1: MyType1;
declare const moreOpt: MoreOptions;
const t2: MyType2 = {...t1, options: {...t1.options, ...moreOpt}};