Easiest way to check for null and empty string on a TypeScript number

Question

I'm surprised this question hasn't been asked, so maybe I'm overlooking the obvious. I have a form field that is supposed to be a number. Its starting value is null, but once a number is entered and cleared, its an empty string. It looks like JavaScript treats "" like 0 for numeric purposes.

So, instead of saying...

if ((this.RetailPrice != null && this.RetailPrice != 0) || this.RetailPrice === 0) {          return this.RetailPrice;        }

Is there a way to extend the TypeScript number type to have a IsNullOrEmpty() method? Or something similar that would simplify this expression?

---

Ultimately, I think I was looking for something as simple as...

if (this.RetailPrice) {  } 

Answer 1

You can simply use typeof. It will check undefined, null, 0 and "" also.

if(typeof RetailPrice!='undefined' && RetailPrice){    return this.RetailPrice; } 

Answer 2

To excludes blank strings as well

if(this.retailPrice && this.retailPrice.trim()){     //Implement your logic here  }