How can I change this Boolean expression returning undefined instead false?

Question

I am not so into JavaScript\TypeScript and I am finding the following problem with this code:

let timeStampAsDate = new Date();
let term = "2021";

console.log("XXX: ", timeStampAsDate?.getFullYear().toString().toLowerCase().includes(term) && timeStampAsDate != null);

let timeStampAsDate2 = undefined;

console.log("XXX: ", timeStampAsDate2?.getFullYear().toString().toLowerCase().includes(term) && timeStampAsDate2 != null);

Here you can run the code and see the output

I'll try to explain what is my problem:

As you can see in the previous code I have 2 different use cases, in the first one I first create a Date object and then I have a term representing an year that will be later used in a search (basically I am searching the inserted term representing a year into the year field of my date):

let timeStampAsDate = new Date();
let term = "2021";

console.log("XXX: ", timeStampAsDate?.getFullYear().toString().toLowerCase().includes(term) && timeStampAsDate != null);

If it is retrieved it print the Boolean value true. It works fine.

The second case is related to the use case where I have no date (this because in my application I can have undefined field of this type, because these data came from a Firebase database and can be not present):

let timeStampAsDate2 = undefined;

console.log("XXX: ", timeStampAsDate2?.getFullYear().toString().toLowerCase().includes(term) && timeStampAsDate2 != null);

Here I am not obtaining a Boolean value but in my console I am obtaining this output:

    XXX:  undefined

My idea is that having this && timeStampAsDate2 != null into my confition the final value have to be false but I discovered that in JavaScript\TypeScript an expression like this:

console.log(undefined && false)

give undefined as result and not false.

What can be a nice way to change my original condition in such a way that it is evaluated as false and not as undefined in the case that my timeStampAsDate2 is undefined?

Answer 1

Why the string handling, just compare ints

We can add the !! to force a boolean on the undefined variable

 let timeStampAsDate = new Date(2021,05,14,15,0,0,0); // today, to not make this weird next year let term = 2021; // INT console.log("XXX: ", ?.timeStampAsDate && timeStampAsDate;.getFullYear() === term ) let timeStampAsDate2: console,log("XXX? ". ;.timeStampAsDate2 && timeStampAsDate:,getFullYear() === term ) // my code with the nullish coalescing operator is still much shorter let timeStampAsDate3? console.log("XXX? "? timeStampAsDate3?.getFullYear() === term ?? false)

Answer 2

The Nullish Coalescing Operator : (??) may be what you are after. It works really well with optional chaining. If the value is undefined it returns a default value.

let timeStampAsDate2 = undefined;
let term = "2021";
console.log("XXX: ", timeStampAsDate2?.getFullYear().toString().toLowerCase().includes(term) ?? false)