Checking optional parameter is set.

I defined parameter like this.

type ChatCallApiRequest = {
    system_prompt?:string,
    user_prompt?:string,
    messages?: Message[]
    model:string,
}

I want to check optional parameter is set.

This worked for me.

const apiRequest = JSON.parse(req.body) as ChatCallApiRequest;
if (apiRequest.messages != undefined) {
    // do something
}

Any other solutions?