How can I fill up missing object parameters in an elegant way?

Issue

I am having trouble using initial parameters (I am not sure if there is a typescript solution or it is just a JavaScript question, so I present you the Javascript equivalent to you):

const helloWorldWithOptions = (options = { a:1, b:2 } ) => {
  console.log("Hello World!")
};

When using the function:

helloWorldWithOptions( {a:4} );

Typescript says that I am missing the object key b when using the function. What I would expect is that js/ts filling up the missing values with the initial parameters. If there is already a state of the art, let me know.

Solution

You can use the Partial type and ... spreading to combine your defaults with the caller's overrides.

TS playground

const defaults = { a: 1, b: 2 };

// Could use a named type instead of `typeof defaults` too.
const helloWorldWithOptions = (options: Partial<typeof defaults> = {}) => {
  const mergedOptions = { ...defaults, ...options };
  console.log(mergedOptions);
};
helloWorldWithOptions({ a: 3 });

Answered By - AKX