Creating objects based on interfaces

Question

After looking at this straightforward code:

interface int1 {
    aa: string,
    bb: number,
}

const obj1:int1 = {}  //#1

function fun(param_obj:int1) {  //#2
}

I am curious as to why the compiler throws an error:

Type '{}' is missing the following properties from type 'int1': aa, bb

at line #1 but doesn't display an error at line #2, even though a new object is being created in both cases?

Answer 1

Answer №1

#1 The code should still throw an error because:

Since the parameters aa and bb are not optional, the object is missing properties defined in the interface int1.

Depending on your intention, you can either make aa and bb optional by defining the interface as follows:

interface int1 {
  aa?: string,
  bb?: number
}

or utilize the Partial keyword from the TypeScript documentation

const obj1: Partial<int1> = {}

As for line #2, as mentioned before, you need to check where you pass in the object.

Answer 2

#1 The code should still throw an error because:

Since the parameters aa and bb are not optional, the object is missing properties defined in the interface int1.

Depending on your intention, you can either make aa and bb optional by defining the interface as follows:

interface int1 {
  aa?: string,
  bb?: number
}

or utilize the Partial keyword from the TypeScript documentation

const obj1: Partial<int1> = {}

As for line #2, as mentioned before, you need to check where you pass in the object.